Which Statement(s) Describe(s) a Second Messengers? (Select All That Apply

Which statement(s) describe(s) a second messengers? (Select all that apply.)

A) They are proteins with active and inhibitory domains.
B) They relay signals from receptors on the plasma membrane to target molecules inside the cell.
C) They activate kinases and phosphatases.
D) They counteract the impact of first messengers.
E) They amplify the impact of first messengers.