EIGRP (Enhanced Interior Gateway Routing Protocol) has a default administrative distance (AD) value of 90 for internal routes. The administrative distance is used to rate the trustworthiness of routing information received from different routing protocols. EIGRP, developed by Cisco, has an AD of 90, which is lower than that of RIP (120) and OSPF (110), making it more preferred if multiple protocols provide a route to the same destination.
Reference: CompTIA Network+ study materials.

Troubleshooting Methodology:
Confirming the Root Cause: After testing and confirming the theory, the next logical step is to address the issue by implementing a solution.
Implementation of the Solution:
Resolve the Issue: Implement the identified solution to rectify the problem. This step involves making necessary changes to the network configuration, replacing faulty hardware, or applying software patches.
Documentation: Document the solution and the steps taken to resolve the issue to provide a reference for future troubleshooting.
Comparison with Other Steps:
Determine Resolution Steps: This is part of the implementation process where specific actions are outlined, but the actual next step after testing is to implement those steps.
Duplicate the Problem in a Lab: This step is typically done earlier in the troubleshooting process to understand the problem, not after confirming the root cause.
Present the Theory for Approval: In some scenarios, presenting the theory might be necessary for major changes, but generally, once the root cause is confirmed, the solution should be implemented.
Final Verification:
After implementing the solution, it is important to verify that the issue is resolved and that normal operations are restored. This may involve monitoring the network and testing to ensure no further issues arise.
Reference:
CompTIA Network+ study materials on troubleshooting methodologies and best practices.

See the answer and solution below
Explanation:

BGP (Border Gateway Protocol) uses an Autonomous System (AS) number for its operations. An AS is a collection of IP networks and routers under the control of a single organization that presents a common routing policy to the Internet. BGP is used to exchange routing information between different ASes on the Internet, making it the only protocol among the listed options that uses an AS number.
Reference: CompTIA Network+ study materials and RFC 4271.

Introduction to Administrative Distance
Administrative distance (AD) is a value used by routers to rank routes from different routing protocols. AD represents the trustworthiness of the source of the route. Lower AD values are more preferred. If a router has multiple routes to a destination from different sources, it will choose the route with the lowest AD.
Static Routes and Backup Routes
When a dynamic routing protocol is not used, static routes can be employed. Static routes are manually configured routes. To ensure a backup route, multiple static routes to the same destination can be configured with different AD values.
Configuring Static Routes with Administrative Distance
The primary route is configured with a lower AD value, making it the preferred route. The backup route is configured with a higher AD value. In the event of the primary route failure, the router will then use the backup route.
Example Configuration:
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ip route 192.168.1.0 255.255.255.0 10.0.0.1 1
ip route 192.168.1.0 255.255.255.0 10.0.0.2 10
In the above example, 192.168.1.0/24 is the destination network.
10.0.0.1 is the next-hop IP address for the primary route with an AD of 1.
10.0.0.2 is the next-hop IP address for the backup route with an AD of 10.
Verification:
After configuration, use the show ip route command to verify that the primary route is in use and the backup route is listed as a candidate for use if the primary route fails.
Reference:
CompTIA Network+ guide explains the concept of administrative distance and its use in static routing configuration (see page Ref 9fasic Configuration Commands).