Consider the given two statements:

I. A double-stranded DNA rich in G and C needs more energy to be broken than one that is rich in A and T.
II. While the ratio of G to C and A to T in an organism's DNA is fixed, the GC content can vary considerably from one DNA to another.

1. Both I and II are correct and II explains I
2. Both I and II are correct but II does not explain I
3. I is correct and II is incorrect
4. Both I and II are incorrect