Correct Answer: D

Rationale: Isotopes of the same element have the same number of protons, which defines the element, but different numbers of neutrons. This difference in neutron count results in isotopes of the same element having different mass numbers. Chemical properties are determined by the arrangement of electrons in an atom, so isotopes of the same element may exhibit slightly different chemical behaviors due to different neutron numbers. The number of electrons can vary in isotopes, affecting their charge. However, the mass number, which is the sum of protons and neutrons, is the same for isotopes of the same element. Therefore, the correct answer is that isotopes of the same element share an identical mass number.

Correct Answer: B

Rationale: The circulatory system, comprising the heart, blood vessels (arteries, veins, and capillaries), and blood, is responsible for transporting blood, oxygen, nutrients, and waste products throughout the body. The lymphatic system aids in maintaining fluid balance and fighting infections; the nervous system transmits signals. The respiratory system facilitates the exchange of oxygen and carbon dioxide in the body, which is distinct from the circulatory system's role in blood transport. Therefore, the correct answer is the Circulatory system (Choice B). Choices A, C, and D are incorrect as they do not pertain to the intricate network of blood vessels responsible for transporting blood throughout the body.

Correct Answer: D

Rationale: The T wave on an ECG corresponds to ventricular repolarization. Following ventricular depolarization, which is represented by the QRS complex, the ventricles undergo repolarization during the T wave. This phase signifies the recovery of ventricular muscle cells as they prepare for the subsequent depolarization cycle. Choices A, B, and C are incorrect because the T wave specifically reflects the repolarization of the ventricles, not the atria or their respective depolarization or repolarization phases.

Correct Answer: C

Rationale: The scrotum is the structure that surrounds and protects the testes. It plays a vital role in maintaining an optimal temperature for sperm production by adjusting the distance of the testes from the body to regulate the effects of external temperature changes. This mechanism helps to safeguard the viability and quality of sperm by ensuring they develop at the right temperature. The epididymis (Choice A) is a coiled tube where sperm mature and are stored, not the structure surrounding the testes. The vas deferens (Choice B) is a duct that carries sperm from the testes to the urethra, not the protective structure around the testes. The prostate gland (Choice D) is part of the male reproductive system, responsible for secreting fluids that nourish and protect sperm, but it is not the structure that surrounds and protects the testes for sperm production.

Correct Answer: B

Rationale: Oxidation is the process where a substance loses electrons. In an oxidation reaction, the substance being oxidized loses electrons, which are gained by another substance. Reduction is the opposite process, where a substance gains electrons. Neutralization is a reaction between an acid and a base to form a salt and water. Precipitation is the formation of a solid from a solution. Therefore, in the context of a chemical reaction involving the loss of electrons, the correct term is oxidation (Choice B).