Purine- Adenine, guanine,pyrimidine- thymine, cytosineAdenine pairs with thymineGuanine pairs with cytosineTherefore the complementary strand to TCG AAG is AGC TTC=========================================================A always pairs with T, and C always pairs with G so the complementary strand is as follows:TCG AAG (Original)AGC TTC (Complementary)GCA TAT