**Core Concept**
The formol ether concentration technique is a laboratory method used to detect parasites, particularly intestinal parasites, in stool samples. This technique relies on the difference in density between the parasites and other stool components. The **formol ether concentration** technique involves the use of a mixture of formalin and ether to separate parasites from debris.

**Why the Correct Answer is Right**
In this technique, the stool sample is mixed with formalin, which helps to preserve the parasites and other organisms. The mixture is then centrifuged, and the supernatant is discarded. Ether is added to the sediment, which helps to dissolve the fatty components of the stool, releasing the parasites. After centrifugation, the parasites are found in the **sediment layer** at the bottom of the tube.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because the parasites are not found in the supernatant after the final centrifugation.
**Option B:** This is incorrect because, although the parasites may initially be mixed with the formalin, they are not found in this layer after the concentration process.
**Option D:** This option is also incorrect as it does not accurately describe the layer where parasites are concentrated.

**Clinical Pearl / High-Yield Fact**
The formol ether concentration technique is a sensitive method for detecting parasites, especially when the parasite load is low. It is essential to carefully examine the sediment layer to identify the parasites.

**Correct Answer:** D. Sediment layer contain the parasites.