Which one is essential fatty acid?
A. Linoleic acid
B. Linolenic acid
C. Arachidonic acid
D. All the above

Hint:Linoleic acid plays a specific function in the protection of cardiac health. Linolenic acid inhibits prostaglandin synthesis resulting in reduced inflammation and prevention. Arachidonic acid is abundant in the brain, muscles, and liver.

Complete answer:
Essential fatty acids are fatty acids that people and other animals have to eat because they are nutritious, but cannot be synthesised. The term 'essential fatty acid', however, does not include fatty acids needed for biological processes which only serve as fuel. Multiple functions serve essential fatty acids in the body.
Linoleic acid plays a specific function in the protection of cardiac health. Randomized clinical tests have shown that the substitution of linoleic acid saturated fat decreases total cholesterol and LDL. Linoleic acid also increases the response to insulin and blood pressure.
Linolenic acid is the dominant fatty acid in the fatty acid group omega-3. It is highly concentrated in selected plant oils and prostaglandin synthesis has been reported to inhibit inflammation and prevention.
Arachidonic acid is a polyunsaturated fatty acid that is found in the brain , muscles, liver and inside the body's membranes, particularly phosphatidylethanolamine, phosphatidylcholine and phosphatidylinositides.

Thus, the correct answer is option D. i.e., All the above.

Note:The two essential fatty acids in the human body are alpha-linolenic acid and linoleic acid. Omega-6 polyunsaturated fatty acid is arachidonic acid. It is found in phospholipids and contributes to membrane formation. The conversion of linoleic acid into arachidonic acid is not an essential amino acid.