Answer:
C. had been honest
Step-by-step explanation:
Option C serves as a context clue that gives us the opposite meaning of the word "dupe" and thus, it helps us find out the true meaning of that word by contrast.
By looking at this phrase, then, we can infer that Kara was trying to deceive, to trick or to swindle Matt because of what comes next: Matthew got angry and wished she had been honest with him, in other words, he wished Kara had done the opposite of what she did.