Which Compound(s) Is/are Involved in Desensitization of The $\beta$ -Adrenergic Receptor?
A)

Multiple Choice

Which compound(s) is/are involved in desensitization of the $\beta$ -adrenergic receptor?

A) $\beta$ -adrenergic receptor kinase
B) arrestin
C) GTPase activating proteins (GAPs)
D) both $\beta$ -adrenergic receptor kinase and arrestin
E) $\beta$ -adrenergic receptor kinase, arrestin, and GTPase activating proteins (GAPs)