Answer:
Thymine
Explanation:
Adenine is a Purines together with Guanine .
Purines always pair with Pyrimidines ; which are cyosine and Thymine.
This is a complementary base pairing that hold the two strands of DNA bases together by weak hydrogen bonds for flexibility and easily unwind during replication
Purines are larger in size beaxuae they have 2 ring structures while Pyrimidines aee smaller because of one ring structure.
Therefore two purines (Adenine and Guanine can not pair together;
It must be a Purines -Pyrimidines pairs.
Therefore Adenine must pair with Thymine and cyosine with Guanine
In RNA, Thymine are replaced with URACIL as Pyrimidines.
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