Answer: C G A C C T A T G G G C... (and so on)
Explanation:
Think of this as one letter representing one half of a pair. The pairs are A and T, and C and G.
When you see a T, its opposite part of the pair is A, and vice versa. The same goes for C and G. To answer this, just write the opposite of what is there.
A -> T
T -> A
and,
C -> G
G -> C
Hope this helps!