Averages and Indices Differ from One Another in That an Index

Averages and indices differ from one another in that an index

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