It is common for companies to place a data cap on the devices they provide to their employees, to control costs. If a user has exceeded the data cap, the phone may no longer allow internet browsing over a cellular connection. This is usually because the cellular data usage has exceeded the allotted amount for the particular plan the device is on, and the service provider has temporarily suspended the data connection.
It is unlikely that the child accidentally connected to a neighbor's WLAN because this would not affect the cellular data connection. Similarly, it is unlikely that the company's group policy has disabled the device, as this would likely affect all devices under the same policy. If the device's plan has been unpaid, the service provider would likely temporarily suspend all services, not just the cellular data connection.
Reference: CompTIA A+ Core 1 Exam Guide, page 329.

The 802.11ax protocol, also known as Wi-Fi 6, provides the fastest bandwidth among the options listed. It can achieve up to 10 Gbps of data transfer rate, using technologies such as OFDMA, MU-MIMO, and 1024-QAM. The 802.11ac protocol, or Wi-Fi 5, is the second fastest, with a maximum of 3.46 Gbps, followed by the 802.11n protocol, or Wi-Fi 4, with a maximum of 600 Mbps. The 802.11a protocol is the slowest, with a maximum of 54 Mbps
https://www.lifewire.com/wireless-standards-802-11a-802-11b-g-n-and-802-11ac-816553

Explanation
The correct answer is D. Cat 6a.
Cat 6a (augmented) is a type of twisted pair cable that supports 10GBASE-T data transmission speed.
10GBASE-T is an Ethernet standard that can deliver 10 gigabits per second (Gbps) over copper cables. Cat 6a can support this speed up to a distance of 100 meters, which is the same as Cat 5e and Cat 6 for lower speeds.
Cat 6a has better shielding and crosstalk prevention than Cat 6, which makes it more suitable for high-frequency signals.
Cat 3, Cat 5, and Cat 5e are not capable of supporting 10GBASE-T data transmission speed. Cat 3 can only support up to 10 Mbps, Cat 5 can only support up to 100 Mbps, and Cat 5e can only support up to 1 Gbps.
These cables have lower bandwidth, higher attenuation, and more interference than Cat 6a.
Reference: Network Cables - CompTIA A+ 220-1101 - 3.1 - Professor Messer IT Certification Training Courses