Answer to first question:
Answer to second question: Thymine
Answer to third queston: c (mismatch repair) and d (base excision repair). Since C is normally paired with G, the T resulting from deamination of C will be located opposite a G. This is a mismatch, the normal substrate for mismatch repair. In addition, there is a DNA N-glycosylase specific for the T in G-T mispairs, so the T can also be repaired by base excision repair. Note: although a mismatch does cause a small structural distortion of the DNA double helix, that distortion is not sufficient to activate nucleotide excision repair.
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