Which is a counterexample to this conjecture?

The sum of any two consecutive integers is a composite number.

A.
16 + 17 = 33

B.
10 + 11 = 21

C.
6 + 7 = 13

D.
7 + 8 = 15

Question

Which is a counterexample to this conjecture? 
 
The sum of any two consecutive integers is a composite number.
 
 A.
16 + 17 = 33
 
 B.
10 + 11 = 21
 
 C.
6 + 7 = 13
 
 D.
7 + 8 = 15

anonymous · Answer

Someone please help?

anonymous · Answer

I think D. because 7 and 8 are consecutive but 15 is not composite (because it is divisible by 5 and 3) so that disproves the conjecture.

anonymous · Answer

do you know what a "counterexample" means?

anonymous · Answer

btw D is not the correct answer

anonymous · Answer

No, not really. I picked C. Is that the right answer?

anonymous · Answer

C proves the conjecture correct, a counter example makes the conjecture false

anonymous · Answer

yes it is C because 
a) that is an example where the sum of two consecutive integers is NOT composite and 
b) the answer is almost always C in a multiple choice problem

anonymous · Answer

Gee, Thanks I have one more.

anonymous · Answer

What is the least common denominator for the fractions   1/6 and 3/4   ?
 
 A.
8
 
 B.
12
 
 C.
18
 
 D.
24

anonymous · Answer

Is it 12?