What are two main types of posttranscriptional modifications that take place in the mrna of eukaryotes? the excision of the introns and the addition of a 7-mg cap to the 3' end.the addition of a poly-t sequence at the 5' end of the gene and the addition of a poly-u tail at the 3' end.the addition of a 7-mg cap at the 5' end of the transcript and the addition of a poly-a sequence at the 3' end of the message.the addition of a poly-a sequence at the 5' end and the addition of a 7-mg cap at the 3' end of the rna transcript.

The correct answer is: The addition of a 7-mG cap at the 5' end of the transcript and the addition of a poly-A sequence at the 3' end of the message

These posttranscriptional processes are called:

•5’ capping - It protects the mRNA from 5' degradation by exonucleases. Cap is also involved in ribosomal binding.

•Polyadenilation or addition of poly(A) tail – It also protects mRNA from degradation of 3’exonucleases.  A long poly(A) tail can also increase translation.

It's A because not all of the species have the same amount of adenine, the moth's is nothing like the rat's, and the amount of guanine is greater than the adenine in a moth.