I belive the answer is d.
We have 20 different amino acids in our bodies.
B. Digestive and Circulatory
Bacteriophage means “eater of bacteria,” and these spidery-looking viruses may be the most abundant life-form on the planet. HIV, Hepatitis C, and Ebola have given viruses a bad name, but microscopic phages are the good guys of the virology world.