To find the complementary sequence, we need to match each nucleotide in the given DNA sequence with its complementary nucleotide. The four nucleotides in DNA are adenine (A), thymine (T), guanine (G), and cytosine (C), and they pair up in a specific way: A pairs with T, and C pairs with G.
Starting with the given sequence:
5'-GACAGTAGTACTAAAT-3'
We can determine the complementary sequence by matching each nucleotide with its complementary nucleotide:
G -> C
A -> T
C -> G
A -> T
G -> C
T -> A
A -> T
G -> C
T -> A
A -> T
The complementary sequence is therefore:
3'-CTGTACTCATGATTTA-5'
Therefore, the answer is A. 3'-CTGTCATCATGATTTA-5'.