Final answer:
The complementary sequence to the DNA strand 5' CGA TTG 3' is 5' GCT AAC 3', following the base pairing rule that adenine pairs with thymine and cytosine pairs with guanine.
Step-by-step explanation:
The subject of this question is DNA base pairing. In a DNA strand, a base pairs with its complement: adenine with thymine and cytosine with guanine. Hence, for the DNA sequence 5' CGA TTG 3', its complementary strand will follow this rule. Therefore, the complementary sequence will be 5' GCT AAC 3'. Hence, the correct answer is B. 5' GCT AAC 3'.
Learn more about DNA base pairing