The entire purpose of route aggregation is summarization - replacing a set of more-specific contributing routes with a single, broader prefix advertised outward - and this summarization inherently hides internal routing instability from external peers: if one of the underlying contributing /24 blocks within a summarized
/16 flaps up and down due to a local link issue, external peers who only see the stable, unchanging /16 aggregate are completely insulated from that churn, since the aggregate itself remains active and advertised as long as at least one contributing route is present, regardless of how much internal fluctuation occurs among the individual contributors. This stability-hiding characteristic is one of the primary operational benefits that motivates using aggregate routes in the first place, confirming that statement as correct. Regarding next-hop behavior, official Juniper documentation is explicit and unambiguous: when an aggregate route is installed in the routing table, Junos assigns it a reject next hop by default, meaning traffic matching only the aggregate (and no more-specific contributor) is dropped and an ICMP unreachable message is returned to the source; a discard next hop is available only as an optional, explicitly configured alternative when silent dropping without ICMP notification is preferred, but it is not the default. Aggregate routes categorically do not advertise their individual contributing routes; suppressing those specific, more-granular prefixes from onward advertisement in favor of the single summary is the aggregate's defining function, directly contradicting the first statement. Reference topics: Junos Enterprise Routing - Protocol Independent Routing, Default Reject Next Hop and Route Summarization Benefits.

Redundant trunk groups are designed to provide link redundancy. If the primary link fails, the secondary link will automatically take over to ensure continued connectivity.
In redundant trunk groups, while regular data traffic is sent over the primary link, Layer 2 control traffic (such as STP, LACP, etc.) is allowed on the secondary link to maintain network stability and protocol operations.
https://www.juniper.net/documentation/us/en/software/junos/multicast-l2/topics/topic-map/redundant-trunk-groups.html

A BGP NOTIFICATION message is one of the four core message types defined in RFC 4271, alongside OPEN, UPDATE, and KEEPALIVE, and it serves a very specific and narrow purpose within the protocol:
whenever a BGP speaker detects an unrecoverable, fatal condition in the session - such as a malformed OPEN message, an unsupported capability, a hold-timer expiration, a finite-state-machine error, or an administratively initiated reset - it transmits a NOTIFICATION message to its peer immediately before closing the underlying TCP connection and tearing down the session entirely. This confirms that a NOTIFICATION always signals the termination of the session upon a fatal error, never a routine, in-session update. Structurally, every NOTIFICATION message carries a defined error code and error subcode field, which together precisely classify the category and specific nature of the fault that triggered the termination (for example, 'Cease' with a subcode indicating administrative shutdown, or 'Update Message Error' with a subcode indicating a malformed attribute), giving the receiving peer's administrator concrete diagnostic information about exactly why the session was torn down. Updating route attributes while keeping a session alive is the role of the UPDATE message, not NOTIFICATION, and refreshing a neighbor's table without resetting the session describes the optional Route Refresh capability (a separate, distinct BGP mechanism), neither of which describes NOTIFICATION's function. Reference topics: Junos Enterprise Routing - BGP, BGP Message Types and the NOTIFICATION Message.

A is correct because you can deploy only stateless firewall filters on an EX Series switch. A stateless firewall filter is a filter that evaluates each packet individually based on the header information, such as source and destination addresses, protocol, and port numbers. A stateless firewall filter does not keep track of the state or context of a packet flow, such as the sequence number, flags, or session information. EX Series switches support only stateless firewall filters, which are also called access control lists (ACLs) or packet filters.
C is correct because you can apply firewall filters to both Layer 2 and Layer 3 traffic on an EX Series switch. Layer 2 traffic is traffic that is switched within a VLAN or a bridge domain, while Layer 3 traffic is traffic that is routed between VLANs or networks. EX Series switches support three types of firewall filters: port (Layer 2) firewall filters, VLAN firewall filters, and router (Layer
3) firewall filters. You can apply these filters to different interfaces and directions to control the traffic entering or exiting the switch.

Because root bridge election is decided primarily by comparing bridge priority values - with the switch advertising the numerically lowest priority always winning, and MAC address serving only as a fallback tiebreaker when priorities are tied - the only deterministic, reliable way to guarantee that a specific switch is elected root regardless of any other switch's hardware characteristics is to explicitly configure that switch with a lower bridge priority than every other participating switch in the topology. Relying on MAC address alone, as the first distractor suggests, is fundamentally unreliable: MAC addresses are burned in at the factory, cannot be predicted or controlled by the administrator, and any future hardware replacement or newly introduced switch with a numerically lower MAC address could unexpectedly seize the root role since MAC comparison only comes into play at equal priority in the first place, meaning a 'highest MAC' strategy does not even align with how the tiebreak actually favors the lowest value. Port priority and port cost are entirely separate STP parameters that influence which port on a non-root switch is selected as its root port, or which port is selected as designated versus blocking on a given segment; neither parameter has any bearing whatsoever on which switch is elected root bridge for the whole topology, since that decision is made purely from the Bridge ID comparison, independent of any per-port settings. Explicitly and deliberately lowering Switch 1's configured bridge priority is the only correct, industry-standard method. Reference topics: Junos Enterprise Switching - Spanning Tree Protocols, Guaranteeing Root Bridge Placement via Bridge Priority.