The total number of genes in a species' genome is not necessarily a good indicat

Tough question. Several of the answers seem reasonable to me. I know I might be too late to help you because you're probably done with school by now (or almost done), but I think the answer is C) alternative splicing. I had to look it up and I found an article I found that I think explains why it's C. Since this is my first post I can't link you directly to it, but I did a Yahoo search for "number of genes as an indicator of complexity" and clicked on the first result from Nature. I'll provide a link assuming this post is accepted. I skimmed the article pretty quickly so I'm not completely sure it answers your question, but I think it's right.

Here's the article I mentioned in my last post.

http://www.nature.com/scitable/topicpage/Eukaryotic-Genome-Complexity-437