Answer:
C) I think because croaks is a verb and the frogs are the subject.
The sentence - Both Lee and I received the e-mail message that you sent us - is written in the active voice. The correct answer is A.
The passive voice would be - The e-mail message that you sent us was received by both Lee and I.
Definitely true. If a sentence doesn't have a verb or subject, it is considered a fragment.