Correct Answer: A

Rationale: - The majority of the body's immune cells are located in the blood. Immune cells, such as white blood cells (leukocytes), circulate throughout the body via the bloodstream to detect and fight off infections and foreign invaders. - While immune cells are also present in other parts of the body like the lymph nodes, spleen, and bone marrow, the blood serves as a primary conduit for immune cells to travel to different tissues and organs to carry out their functions. - The brain (option B) is protected by the blood-brain barrier, which limits the entry of immune cells into the brain to prevent inflammation and damage. - The skin (option C) contains immune cells like Langerhans cells that help protect against pathogens, but the largest concentration of immune cells is found in the blood. - The large intestine (option D) also houses a significant amount of immune cells due to its role in interacting with the external environment through the gut-associated lymphoid tissue, but the primary location for most of the body's immune cells is the blood.

Correct Answer: A

Rationale: The correct answer is A: Ligament. Ligaments are tough bands of tissue that connect bones to other bones at joints, providing stability and support. In the case of the wrist or ankle, ligaments play a crucial role in maintaining the structural integrity and allowing for proper movement of these joints. Tendons (option B) connect muscles to bones, not bones to bones. Fascia (option C) is a connective tissue that surrounds muscles and other structures, not connecting bones at joints. A synovial joint (option D) is a type of joint that allows for movement between bones, but it is not the flexible connection between bones at the wrist or ankle.

Correct Answer: C

Rationale: Sarcomeres are the smallest contractile units within muscle cells. They consist of overlapping filaments of actin and myosin proteins, which interact to produce muscle contractions. Myocytes are the entire muscle cells, myofibrils are bundles of protein filaments found within muscle cells, and tendons are tough connective tissues that connect muscles to bones. Therefore, sarcomeres specifically represent the contractile units responsible for muscle contraction, making them the correct answer in this context.

Correct Answer: A

Rationale: The wavelength of a wave represents the distance between two successive identical points on a wave, such as two crests or two troughs. It is typically measured in meters and is a fundamental characteristic of a wave, influencing its properties and behavior. Wavelength is crucial in wave physics, affecting phenomena like interference, diffraction, and the wave's speed in a medium. Amplitude refers to the maximum displacement of a wave from its rest position, frequency is the number of complete oscillations a wave makes in a given time, and period is the time it takes for a wave to complete one full cycle. These properties are different from wavelength and serve distinct purposes in describing waves.

Correct Answer: A

Rationale: The correct answer is Amplitude. Amplitude is the property of a wave that determines its loudness in sound waves. The greater the amplitude of a sound wave, the louder the sound will be perceived. Wavelength and frequency are related to the pitch of the sound, with wavelength affecting the tone quality and frequency determining the pitch. Speed, on the other hand, is a characteristic of how fast the wave travels through a medium and does not directly influence the loudness of the sound.