Which of the following statements is TRUE?

a. Prebiotics are indigestible foods, primarily soluble fibers, that stimulate the growth of certain strains of bacteria in the large intestine and provide health benefits to the host.
b. When comparing methods of predicting disease, measuring waist circumference is considered a better measurement than the waist-to-hip ratio.
c. Nine out of the twenty amino acids in the body are called nonessential amino acids because the body can synthesize them.
d. The endocrine system is composed of white blood cells, lymphatic tissue, and marrow, and is responsible for immunity.