So you probably know that the four bases are Adenine, Thymine, Cytosine, and Guanine. You probably also know that these bases pair up. Adenine ALWAYS pairs with thymine when you are talking about DNA strands. Cytosine ALWAYS pairs with Guanine. So, the strand AGTAAC, which is also Adenine, Guanine, Thymine, Adenine, Adenine, Cytosine, will be paired with Thymine, Cytosine, Adenine, Thymine, Thymine, Guanine, or TCATTG, which is C. Have a good day!