12) B & C

The best way to answer this question is to multiply all of the options by 3 and see if the scores obtained by the remaining questions can be manipulated to give 18.

A: 5 x 3 = 15
This is 3 points less than 18. However you only gain points by answering a question correctly. Since option A allows only 5 questions to be correct, John cannot get anymore points. So this option is incorrect.

B: 6 x 3 = 18
We have already reached 18. Now it is a possibility that he did not answer the remaining questions and got 0 points. So this is one of the correct answers.

C: 7 x 3 = 21
Now, this is 3 points more than the required number 18. Also, there are 5 remaining question since the quiz only consists of 12 question. It is possible that out of the 5, he got 3 incorrect and didn’t answer the other 2. Final calculation:
Correct = 7×3 = 21
Incorrect = 3x(-1) = -3
No answer = 2×0 = 0
Total = 21-3 = 18
So C an also be correct

D: 8 x 3 = 24
Remaining questions = 4
Points needed to get to 18 = (-6)
If he gets the remaining 4 questions incorrect, final points = 24-4 = 20
This does not lead to the required number 18, so D is incorrect

E: Same principle applies to E. It is not possible to obtain the number 18