Which of the Following Might Explain Why Most People Are

Which of the following might explain why most people are sick more often as children than as adults in their 20s through 50s?

A) The thymus is so active in children that it fights bacteria so hard that it produces strong symptoms of disease.
B) We build up many varieties of memory lymphocytes during childhood, providing immunity to more and more antigens during adulthood.
C) The immune system does not appear until the preteen years.
D) Because of their small size, childrenʹs bodies cannot contain as much lymphoid tissue as those of adults.