The Half-Life of a Reaction Is

The half-life of a reaction is

A) twice as long for a second-order reaction as it is for a first-order reaction.
B) one-half of the time the reaction will take to go to completion.
C) how long the reaction can run before stopping.
D) the time it takes for the amount of product formed to equal half the initial amount of reactant.
E) the time it takes for the reactant concentration to decrease to one-half of its initial value.