The correct answer is B.
According to base pairing rules, A will always pair with T and and G will always pair with C. This pairing happens in DNA.
When it comes to RNA, there is a slight difference. Thymine is never found in RNA but is replaced with Uracil. So instead of Adenine pairing with Thymine, it will be Uracil which takes the place of Thymine.
It is important to note that Thymine in DNA will code for Adenine in RNA because Adenine is found in RNA base sequence. However whenever Adenine in DNA wants to code for a complementary base to copy on RNA, then Adenine will call for Uracil, not Thymine.