Which of the following addresses are not valid Class A network IDs? (Choose all that apply)

(A) 1.0.0.0
(B) 5.0.0.0
(C) 140.0.0.0
(D) 127.0.0.0
(E) 9.0.0.0
(F) 195.0.0.0

C, D and F are the correct answers.

Class A networks have the first octet in the range of 1–126, inclusive, and their network IDs have a 0 in the last three octets.

Invalid Class A network IDs are:
140.0.0.0
127.0.0.0
195.0.0.0