Final answer:
The post-transcriptional modifications in eukaryotic mRNAs include the addition of a 5' methylguanosine cap, addition of a 3' poly-A tail, and c. the removal of introns.
Step-by-step explanation:
The correct answer to the question regarding post-transcriptional modifications occurring in eukaryotic mRNAs is the option c: cap addition and removal of introns.
Eukaryotic pre-mRNAs undergo several post-transcriptional modifications, which include the addition of a 5' 7-methylguanosine cap and a 3' poly-A tail, along with splicing to remove introns.
The 5' cap and the poly-A tail both play roles in protecting the mRNA from degradation and assisting its export from the nucleus, as well as in the initiation of translation by ribosomes.