Responding to both multiple stimuli and response possibilities have been shown to be affected by blood alcohol concentration of as low as .04. this is called

Answer – Choice or complex reaction time

Blood alcohol concentration of as low as .04 can significantly affect general alertness, such that a person’s ability to respond to both multiple stimuli and response possibilities have been shown to be affected when the choice reaction time (also called complex reaction time) is tested.

Awould be the most dangerous

Yes, this is very true. specifically causing damage in the  dentrite.