Which statement correctly defines complementary strands?

• A. The sequence of the DNA on one strand that chemically matches the sequence on the other strand
• B. The two DNA strands are identical
• C. RNA sequences pair with DNA
• D. Proteins that bind to DNA

Answer: (A)

Complementary strands are two DNA strands that pair with each other through specific base pairing. Each base on one strand has a designated partner on the other: A pairs with T, and G pairs with C. Because of this, the sequence on one strand determines the sequence on the other, though read in the opposite direction, so the strands are complementary rather than identical. The statement reflects this base-pairing rule, describing how the sequence on one strand chemically matches the sequence on the other. The other options miss the idea: the strands are not identical, RNA–DNA pairing isn’t what defines DNA complementarity, and proteins binding to DNA aren’t about complementary base pairing.