In Order to Determine Brain Efficiency, Reaction Times Have Been

In order to determine brain efficiency, reaction times have been measured by which of the following techniques?

A) the amount of time it takes a person to press a key to indicate whether a line segment is shorter than another
B) the amount of time between blinks of the eye when puffs of air make contact with the eye
C) the amount of parasympathetic nervous system activity shown following exposure to a surprise
D) the amount of time it takes a person to become classically conditioned to a buzzer