Answer:
TGCAGCTAGTCG
Explanation:
For every T, the complementary strand will have A
For every A, the complementary strand will have T
For every C, the complementary strand will have G
For every G, the complementary strand will have C
SO,
ACGTCGATCAGC
TGCAGCTAGTCG
A always bonds with T and C always bonds with G ... a useful pneumoinc is "Apple Tree, Car Garage"
