Which of the Following Statements Is TRUE

Which of the following statements is TRUE?

A) Circulating antibody concentrations are largely unchanged in response to brief and prolonged intensive exercise
B) Circulating antibody concentrations tend to fall after brief and prolonged intensive exercise
C) Mitogen-stimulated IgM concentration appears to decrease in response to exercise independently of changes in T or B cell number
D) Antibody responses to vaccination are generally increased after prolonged exercise
E) IgG antibodies are converted to IgM antibodies following prolonged exercise