One of the Advantages of Conducting a Longitudinal Study Instead

One of the advantages of conducting a longitudinal study instead of a cross-sectional study is that:

A) it allows researchers to follow groups long enough to assess both short-term and long-term effects.
B) it produces results that are almost always generalizable to the larger population.
C) it is often inexpensive and the least time consuming of all research designs.
D) it rarely suffers from the third variable problem and can accurately separate causes from consequences.