**Core Concept**
Diatoms are a type of algae that are commonly found in aquatic environments. The diatoms test is used to detect the presence of diatoms in water samples, which can be an indicator of recent drowning. The test relies on the fact that diatoms in the sputum or blood of a deceased person are indicative of inhalation of water containing diatoms.

**Why the Correct Answer is Right**
The best site for taking a sample for the diatoms test is the stomach contents. When a person drowns, water enters the stomach and the diatoms present in the water are ingested along with it. The stomach contents can be examined for the presence of diatoms, which can provide evidence of drowning. The stomach contents are the best site for sampling because diatoms are more likely to be present in the stomach than in other parts of the body.

**Why Each Wrong Option is Incorrect**
* **Option A:** The lungs are not the best site for taking a sample for the diatoms test because while diatoms may be present in the lungs, they may also be present due to other causes such as aspiration.
* **Option B:** The heart blood is not a reliable sample for the diatoms test because diatoms may not be present in the blood in sufficient quantities to be detected.
* **Option D:** The intestine is not the best site for taking a sample for the diatoms test because while diatoms may be present in the intestine, they may also be present due to other causes such as ingestion of contaminated food or water.

**Clinical Pearl / High-Yield Fact**
The diatoms test is not foolproof and can be influenced by various factors such as the presence of other algae, contamination of the sample, and the time elapsed since drowning. Therefore, the results of the diatoms test should be considered in conjunction with other evidence and clinical findings.

**Correct Answer:** C.