Which of the following conditions point to a network interface device as being a bottleneck?

A.
An output packet queue of 2 and more.

B.
An output packet queue of 1 and under.

C.
The network is constantly being used at the maximum transfer rate.

D.
A and C

Explanation:
The network interface device is the bottleneck when the length of the output packet queue is 2 and more, and the network is constantly being used at the maximum transfer rate.
References:
Charles J. Brooks, Server+ Certification Exam Cram 2 (Exam SK0-002), QUE Publishing, Indianapolis, 2006, pp. 534-536.