Step 1: Purpose of descriptive research.
Descriptive research focuses on describing characteristics, measuring associations, and gathering detailed factual information. It does not establish cause-and-effect relationships.
Step 2: Elimination.
- (a) Correct use of descriptive research — describing characteristics of groups.
- (b) Also correct — can measure associations.
- (d) Correct — surveys and opinion polls are part of descriptive research.
- (c) Wrong for descriptive research — identifying cause and effect is causal research, not descriptive.
\[
\boxed{(c)}
\]