Correct Answer: D

Rationale: The reticular formation is a network of neurons located in the brainstem that plays a crucial role in regulating arousal and consciousness. It generates the rhythmic electrical activity responsible for brain waves, which are measured using electroencephalography (EEG). The cerebrum, thalamus, and hypothalamus do not primarily generate brain waves; they have other specialized functions within the brain. The cerebrum is responsible for higher brain functions such as thinking and voluntary movements. The thalamus acts as a relay station for sensory information. The hypothalamus is involved in various functions such as regulating body temperature, hunger, and hormonal activities.

Correct Answer: C

Rationale: Merkel cells are specialized touch receptors located in the epidermis of the skin. Their primary function is to perceive light touch and pressure. They play a crucial role in the sensory perception of touch stimuli. Option A, melanin production, is incorrect because Merkel cells are not involved in producing melanin. Option B, temperature sensation, is incorrect as Merkel cells are not specialized for sensing temperature. Option D, immune defense, is also incorrect as Merkel cells do not have a role in immune defense mechanisms.

Correct Answer: B

Rationale: Antigenic variation is a strategy used by some viruses to evade the host's immune response. By constantly changing their surface antigens, viruses can avoid recognition and destruction by the immune system. This allows the virus to persist in the host and continue replicating, leading to prolonged infection and potential transmission to other hosts. Antigenic variation does not directly involve the production of toxins, survival outside a host, or rapid replication, making options A, C, and D incorrect in this context.

Correct Answer: B

Rationale: Toluene is an aromatic compound due to its benzene ring structure, which satisfies the criteria of aromaticity. Aromatic compounds contain conjugated pi electrons in a ring structure, providing extra stability. Ethanol, acetone, and butanal are not aromatic compounds as they do not possess a benzene ring or meet the aromaticity criteria. Ethanol is an alcohol, acetone is a ketone, and butanal is an aldehyde, none of which have the characteristic benzene ring structure of aromatic compounds.

Correct Answer: B

Rationale: Cartilage is a flexible connective tissue found in the joints between bones. It provides cushioning and support for the bones, allowing smooth movement and reducing friction between them. Cartilage acts as a shock absorber and helps maintain the structural integrity of the joints. Choices A, C, and D are incorrect because cartilage is not typically found in the center of long bones, muscle tissue, or the walls of blood vessels. Cartilage primarily functions in providing structural support and flexibility in joints.