Verified answer

420 amino acids means that the mRNA has to be at least 1260 nucleotides long. That rules out A, B and E.

Now, the decision is between C and D. It's important to note that we're talking about a eukaryotic organism. Eukeryotes often have introns; sequences in their genes that are spliced out before translation occurs. That would make the gene (and the pre-mRNA) bigger than 1260.

The alternative is that the gene and the mRNA are both exactly 1260 nucleotides long. Because of the prevalence of introns, I would judge that to be unlikely. It's probably there to throw you off if you forget to think about other processes than simple transcription/translation.

So, I'd go with C

http://en.wikipedia.org/wiki/RNA_splicing

this is so basic it scares me you are doing a biology course -.-

mRNA because it doesnt contain introns.