If transition mutation happens to the third position of a DNA base sequence GTC, which base can be substituted in the position of that mutated cytosine?

A transition is a point mutation that changes a purine nucleotide to another purine (A ↔ G) or a pyrimidine nucleotide to another pyrimidine (C ↔ T). So here in the given DNA sequence the transition mutation makes changes in the third position where the pyrimidine cytosine is present. As a result this cytosine is substituted by another pyrimidine that is thymine. The DNA base sequence GTC which codes for the amino acid valine is changed to GTT that also codes for the same amino acid valine.