Correct Answer: D

Rationale: A) Insulin is a hormone, not a fibrous protein. It is produced in the pancreas and regulates blood sugar levels. B) Keratin is a fibrous structural protein found in hair, nails, and the outer skin layer, providing strength and protection. C) Hemoglobin is a globular protein in red blood cells responsible for oxygen transport; it is not fibrous. D) Collagen is a fibrous protein found in tendons, ligaments, and skin, offering strength and structure to connective tissues. Therefore, the correct answer is collagen, making it the main component of various connective tissues.

Correct Answer: B

Rationale: Insulin is the hormone responsible for lowering blood sugar levels. It is produced by the pancreas and facilitates the entry of glucose into cells, thereby reducing blood sugar levels. Glucagon, adrenaline, and cortisol have roles in increasing blood sugar levels through various mechanisms. Glucagon raises blood sugar levels by stimulating the liver to release stored glucose, adrenaline increases blood sugar in fight-or-flight responses, and cortisol raises blood sugar levels as part of the stress response. Therefore, in the context of lowering blood sugar levels, insulin is the correct answer.

Correct Answer: C

Rationale: Gold is the correct answer. Gold is a popular choice for jewelry due to its exceptional malleability, allowing it to be easily shaped into intricate designs. Moreover, gold is resistant to tarnish, ensuring the jewelry retains its beauty over time. Iron is not commonly used in jewelry due to its susceptibility to rusting. Copper is also not as popular in jewelry making as gold due to its tendency to tarnish and cause skin discoloration. While silver is used in jewelry, it is more prone to tarnish compared to gold, making it less ideal for long-lasting pieces.

Correct Answer: A

Rationale: The correct answer is A: Stapes (Middle ear bone). The stapes, located in the middle ear, is indeed the smallest bone in the human body. Despite its small size, the stapes is vital for hearing as it transmits and amplifies sound vibrations, contributing significantly to auditory perception. Choices B, C, and D are incorrect. The patella (kneecap) is the largest sesamoid bone in the human body, not the smallest bone. Phalanges are the bones in fingers and toes, not the smallest bone overall. Ribs are long bones that protect the chest cavity, not the smallest bone in the body.

Correct Answer: B

Rationale: Benzene is indeed an example of an aromatic hydrocarbon. Aromatic hydrocarbons are characterized by having a cyclic structure with alternating single and double bonds (pi bonds). Benzene fits this description, making it aromatic. On the other hand, ethane, propane, and butene are aliphatic hydrocarbons, which do not have the distinct cyclic structure of aromatic hydrocarbons. Ethane, propane, and butene are aliphatic hydrocarbons, which contain only single bonds and are not cyclic in nature. Therefore, they are not examples of aromatic hydrocarbons.