**Core Concept**
A polygraph test, also known as a lie detector test, is a method used to detect deception by measuring various physiological responses to a series of questions. The test measures several physiological parameters, including cardiovascular activity, respiratory rate, skin conductivity, and muscle activity.

**Why the Correct Answer is Right**
GSR stands for Galvanic Skin Response, which refers to the measurement of the electrical conductivity of the skin. This is done by placing electrodes on the fingertips to measure the subtle changes in skin conductivity when a person is asked a question. The GSR parameter is used to assess the person's emotional state and detect any signs of deception.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not relate to the polygraph test or the physiological parameters measured during the test.
**Option B:** This option is incorrect because it is not a valid abbreviation for any of the physiological parameters measured during a polygraph test.

**Clinical Pearl / High-Yield Fact**
The polygraph test is not admissible as evidence in most courts, as its reliability and validity have been questioned. However, it is still widely used in investigative and security settings to gather information and detect potential deception.

**Correct Answer: C. Galvanic Skin Response.**