Question

adenine (a) pairs with a: cytosine (c) B: Guanine (g) C: Thymine (T)

Answer 1

Adenine pairs with Thymine and Guanine pairs with Cytosine. I remember this by the car (C) goes in the garage (G). Then A and T are the only ones left, so they pair together.

Answer 2

Adenine pairs with Thymine because they have a common hydrogen bond.
Guanine and Cytosine are the other pair, don't forget.