If a DNA strand has a base sequence TCA, its complementary strand must be

If a DNA strand has a base sequence TCA, its complementary strand must be AGT. In DNA, the four nitrogenous bases (adenine, thymine, cytosine, and guanine) pair up in a specific way, with adenine always pairing with thymine and cytosine always pairing with guanine. Therefore, in the complementary strand, each base that pairs with T (thymine) must be A (adenine), each base that pairs with C (cytosine) must be G (guanine), and each base that pairs with A (adenine) must be T (thymine). So, the complementary strand to TCA is AGT, because A pairs with T, G pairs with C, and T pairs with A.