The correct option is A Nucleus
Eukaryotic mRNA is synthesized in the nucleus; the original product, primary transcript, is processed through capping, splicing and tailing. Splicing is the removal of introns from the primary transcript and ligation of exons to form a continuous sequence specifying a functional polypeptide. Capping of eukaryotic mRNAs refers to the addition of 7-Methylguanosine to the 5’ end of almost all eukaryotic mRNAs in an unusual 5’,5’- triphosphate linkage. Since mRNA translocation to the cytoplasm, where it serves as the template for protein synthesis, is coupled with processing; it occurs in nucleus itself. Ribosomes are the large cytoplasmic complex of rRNA and a set of protein and serve as the site for protein synthesis. ER is a eukaryotic organelle with a network of tubules, vesicles and cisternae within the cells. It serves to synthesis and transport of proteins and lipids. Dictyosomes are stacks of flat, membrane-bound cavities and comprise Golgi apparatus. They serve in storage, modification, sorting, and packaging of proteins into vesicles for transport. The correct answer is A.