The purpose of operational definitions in science is to:

A) keep participants from knowing which treatment group they are in.
B) reduce demand characteristics.
C) increase ecological validity.
D) carefully define terms and variables so they can be objectively studied.

Answer: D
Rationale: Operational definitions are statements that describe the procedures (or operations) and specific measures that are used to record observations. By carefully defining psychological terms such as "intelligence" or "happiness," everyone can understand exactly how these variables are being objectively measured.