The best answer is A.
The shape of a protein is determined by its primary structure. The primary structure is the sequence of amino acids in each polypeptide chain which make up a protein.
The sequence of amino acids is basically a list of amino acids that are linked to each other to form a chain which is known as a polypeptide chain.
The structure of the finished protein will depend largely on the first (primary) chain of amino acids to be produced to make up that protein.
