**Core Concept**
Heat treatment is a process used to inactivate proteins, enzymes, and other biological molecules. The temperature and duration of heat treatment can vary depending on the specific application and the desired outcome. In this context, heating at 60degC for 30 minutes is used to inactivate certain biological molecules, leading to their isolation.

**Why the Correct Answer is Right**
The correct answer is **C. Proteins**. Heating at 60degC for 30 minutes is sufficient to denature and inactivate proteins, making them precipitate out of solution. This is because proteins have a relatively low melting point and are susceptible to heat denaturation. The heat treatment disrupts the hydrogen bonds and hydrophobic interactions that hold the protein structure together, leading to the formation of insoluble aggregates.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because nucleic acids, such as DNA and RNA, are more resistant to heat denaturation than proteins. They require higher temperatures and longer incubation times to be inactivated.
**Option B:** This option is incorrect because carbohydrates, such as starch and cellulose, are not typically inactivated by heat treatment at 60degC. They may undergo gelatinization or other changes, but they are not isolated by this process.
**Option D:** This option is incorrect because lipids, such as fats and oils, are not inactivated by heat treatment at 60degC. They may undergo melting or other changes, but they are not isolated by this process.

**Clinical Pearl / High-Yield Fact**
It's worth noting that heat treatment can be used to inactivate enzymes and other biological molecules in a variety of applications, including food processing, medical sterilization, and laboratory techniques. The specific temperature and duration of heat treatment will depend on the desired outcome and the specific molecules being targeted.

**Correct Answer:** C. Proteins