**Core Concept**
The Cavett test is a method used for detecting the presence of certain substances in the blood, specifically focusing on the measurement of the velocity of sound in the blood. This test relies on the principle that the velocity of sound in the blood is altered by the presence of certain compounds, allowing for their detection.

**Why the Correct Answer is Right**
The Cavett test is specifically used for detecting lipids in the blood. The test works by measuring the velocity of sound in the blood, which is affected by the presence of lipids. When lipids are present in the blood, they alter the velocity of sound, allowing for their detection. The Cavett test is a useful tool for diagnosing and monitoring conditions such as hyperlipidemia.

**Why Each Wrong Option is Incorrect**
**Option A:** The correct answer is not a substance that affects the velocity of sound in the blood.
**Option B:** The Cavett test is not used for detecting glucose in the blood.
**Option C:** The correct answer is not a compound that would be detected by measuring the velocity of sound in the blood.

**Clinical Pearl / High-Yield Fact**
The Cavett test is a useful tool for detecting lipids in the blood, but it is not as commonly used as other methods such as the lipid profile. It is essential to remember that the Cavett test is specific to detecting lipids and should not be used for detecting other substances in the blood.

**Correct Answer:** D. Lipids