Describe three of the functions of DNA that Watson and Crick's model provided an elegant solution for.

1. Replication by means of complementary base-pairing. (This is mentioned in the W&C paper).

I think that's about it. Since you have to come up with two more, try these:

2. Transcription to RNA, also by means of complementary base-pairing

3. Not getting into a tangled mess. The double-stranded nature meant that the bases weren't "open" which would lead to folding back on itself to make partially double-stranded regions the way RNA does.