To Do a One-Tail T Test, as Opposed to a Two-Tail

Multiple Choice

To do a one-tail t test, as opposed to a two-tail,

A) the direction of the difference must always be specified beforehand
B) the direction of the difference need only be specified after null has been rejected
C) the direction of the difference must only be specified when null is accepted
D) the direction of the difference becomes irrelevant