Which of the Following Statements Is True

Multiple Choice

Which of the following statements is true?

A) Phosphorylation by protein kinase can stimulate or inhibit the activity of effector proteins
B) Ca2+ and cyclic AMP are second messengers
C) Phosphodiesterase converts GMP into cGMP
D) Both phosphorylation by protein kinase can stimulate or inhibit the activity of effector proteins and Ca2+ and cyclic AMP are second messengers are true
E) All of the choices are true