Question

Which is a counterexample to this 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

Answer 1

please explain

Answer 2

C because 13 is not a composite number and cannot be divided by any number but 1

Answer 3

13 is a prime number

Answer 4

the number which has only two factors i.e 1 and itself is called a prime