The answer is the fourth one (d): Lipid.
Explanation for each option:
a. Nucleic acid - This class of organic compounds includes DNA and RNA, which are responsible for storing and transmitting genetic information. They do not include steroids and triglycerides.
b. Protein - Proteins are composed of amino acids and serve various functions in the body, such as catalyzing biochemical reactions and providing structural support. They do not include steroids and triglycerides.
c. Carbohydrate - Carbohydrates are organic compounds made up of sugar molecules and are primarily used for energy. They do not include steroids and triglycerides.
d. Lipid - Lipids are a diverse group of organic compounds that are insoluble in water. This class includes fats, oils, waxes, phospholipids, steroids, and triglycerides. Therefore, steroids and triglycerides are both classified as lipids.
Summary:
Steroids and triglycerides are both classified as lipids, making option d the correct answer.