Final answer:
If 30% of the bases in a DNA molecule are adenine, then the percentage of thymine is also 30% since adenine and thymine pair together and are present in equal amounts.
Step-by-step explanation:
If 30% of the bases within a DNA molecule are adenine, then the percentage of thymine must also be 30%. This is because adenine (A) always pairs with thymine (T) in DNA strands, thus they are present in equal amounts. Given that DNA is a double-stranded molecule where the bases pair with each other, A with T and cytosine (C) with guanine (G), the percentage of adenine will equal the percentage of thymine. Therefore, the correct answer is C) 30%.