Basically you have to match up the letters. Here is something u can use to help remember how to pair the nucleic acids. Cars in the garage (cytosine pares with guanine and nothing else) and apples in the trees (adenine pairs with thymine) thymine becomes uracil during the process of RNA. Therefore, segment 3 would be the one with the error because the C representing cytosine does not pair with the G representing guanine.
