Averages and Indexes Differ from One Another in That an Index

Averages and indexes differ from one another in that an index

A) is the arithmetic average price behavior of a group of stocks at a given point in time.
B) measures the current price behavior of a group of stocks in relation to a base value set at an earlier point in time.
C) is of value in-and-of itself, whereas an average must be compared to a historical figure to have any meaning.
D) always moves up before a corresponding average moves up, and always moves down before a corresponding average moves down.