正解:A
The configured address 192.168.16.143 with a /28 mask is the broadcast address of its subnet, so the router correctly rejects it with a bad-mask message. A /28 mask creates blocks of 16 addresses. In the 192.168.16.128
/28 subnet, the usable host range is 192.168.16.129 through 192.168.16.142, and 192.168.16.143 is the directed broadcast address. A broadcast address cannot be assigned to a router interface because it represents all hosts in that subnet, not one device. The issue is not that the router lacks /28 support, and it is not caused by private addressing. It is also not the network address; the network address would be 192.168.16.128.
CCNA 200-301 v1.1 Network Fundamentals requires precise subnet boundary recognition. The verified answer is A because the address shown in the exhibit is the subnet broadcast address. Reference: Cisco IPv4 subnetting fundamentals and interface address validation behavior.