Leo Drank Quite a Lot at the "Biggest Party of the Year

Multiple Choice

Leo drank quite a lot at the "biggest party of the year." Later, he had trouble falling asleep, so he took a Valium. If he dies from respiratory failure during the night, it is probably because the alcohol and Valium created a(n) :

A) synergistic effect.
B) antagonistic action.
C) complementary action.
D) cross-tolerance effect.