**Core Concept**
Eicosapentaenoic acid (EPA) is an omega-3 fatty acid that plays a crucial role in reducing inflammation and improving cardiovascular health. It is a polyunsaturated fatty acid that is essential for various bodily functions, including heart health and brain function.

**Why the Correct Answer is Right**
EPA is richly found in fatty fish, such as salmon, mackerel, and sardines. These fish are high in omega-3 fatty acids, particularly EPA and docosahexaenoic acid (DHA). The intake of EPA and DHA has been associated with various health benefits, including reduced triglyceride levels, improved blood lipid profiles, and decreased inflammation. The mechanism of action of EPA involves the inhibition of inflammatory pathways, such as the cyclooxygenase (COX) and lipoxygenase (LOX) pathways.

**Why Each Wrong Option is Incorrect**
**Option A:** Nuts and seeds are rich sources of other types of fatty acids, such as alpha-linolenic acid (ALA), but they are not the richest sources of EPA.

**Option B:** Olive oil is high in monounsaturated fatty acids, which have different health benefits than EPA.

**Option C:** Coconut oil is high in saturated fatty acids, which have been associated with increased risk of cardiovascular disease.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the richest sources of EPA are fatty fish, and the health benefits of EPA are most pronounced when consumed in the form of whole foods, rather than supplements.

**Correct Answer:** D. Fatty fish.