There are four bases in a strand of DNA: Adenine, Guanine, Thymine, and Cytosine. Adenine will always pair with Thymine, and Guanine will always pair with Cytosine. We can use this to figure out the corresponding half of the given DNA Segment.
We are given the following segment: AGT CAC GCA. Using the above rule of which bases pair together, let's figure out the corresponding half of the segment.
AGT CAC GCA
TCA GTG CGT
The solution is B.