Question

what is unique about the experimental design of an observational study?
a. evidence is used to test a hypothesis.
b. experimental subjects are left free of manipulation.
c. data is collected and analyzed for patterns.
d. knowledge about a living thing is generated.

Explanation:

In an observational study, the key characteristic is that researchers observe subjects without manipulating them. Option A is common in many studies (not unique to observational). Option C is also done in other study types. Option D is too narrow (not just about living things). Observational studies focus on natural behavior (no manipulation), so B is correct.

Answer:

B. Experimental subjects are left free of manipulation.