Question

The boys don’t know if __________ going to enter the talent contest or not.

Answer 1

c) they're

They're = they are. There is an apostrophe in place of the a. Hope this helped :)

Answer 2

They boys do not know if they are going to enter the talent contest or not. 
The contraction of "they are" is "they're".

The correct choice is C. They're.

Hope this helps =)