The answer is UAC.
In the RNA, base complements are adenine - uracil (A-U) and guanine -cytosine (G-C). So, when in the process of translation, anticodons of tRNA pairs with codons of mRNA, the complementary bases will pair. So, adenine in tRNA will pair uracil in mRNA (A → U), uracil in tRNA will pair adenine in mRNA (U → A), and guanine in tRNA will pair cytosine in mRNA (G → C):
tRNA: A U G
mRNA: U A C
