The best choice is A.
A gene is a specific sequence of nucleotides in DNA or RNA that is located usually on a chromosome and that specifies the structure of a particular polypeptide and especially a protein, or controls the function of other genetic material.
Information from the gene is copied (transcribed) on mRNA in the nucleus. mRNA then leaves the nucleus and enters the cytoplasm where it attaches to a ribosome. The information on the attached mRNA is decoded (translated) by tRNA which then fetches the amino acids according to this information and brings them to the ribosome where they are linked together to form the specified protein.
