Correct Answer: B

Rationale: The word 'intramuscularly' in the sentence indicates that the vaccine should be used by injection directly into the muscles. This means the correct meaning is 'into muscles,' making option B the most suitable choice. Choices A, C, and D are incorrect because 'intramuscularly' specifically refers to administering something inside the muscle, not between muscles, without muscles, or on top of muscles.

Correct Answer: D

Rationale: The correct answer is D, 'recurring.' A chronic condition is one that is ongoing or long-lasting, implying that it persists or recurs over a prolonged period of time. Choices A, B, and C are incorrect because chronicity does not necessarily imply harmlessness, criticality, or contagion; rather, it refers to the persistent or recurring nature of the condition.

Correct Answer: A

Rationale: The word 'derivative' in this sentence means that the professor's lecture was not original, but instead heavily based on or closely imitating something else. Therefore, the correct meaning is 'unoriginal.' Choices B, C, and D are incorrect. 'Monotonous' means lacking in variety and boringly repetitive, 'condescending' means showing a superior attitude, and 'long-winded' means using more words than necessary.

Correct Answer: C

Rationale: In the context of the sentence, the word 'placebo' refers to a substance or treatment that resembles a real medical treatment but has no therapeutic effect. It is used as a standard against which the effects of the experimental drug are compared. A placebo is typically included in a control group in medical research to evaluate the actual effects of the experimental drug. Therefore, in this scenario, the placebo serves as a control to gauge the effectiveness of the experimental drug, making choice C the correct answer. Choices A, B, and D are incorrect because a placebo is not a fallback, substitute, or curative treatment in this context.

Correct Answer: C

Rationale: The word 'contemptuous' means showing disdain or scorn for something or someone. Therefore, the word 'scornful' is the most closely related synonym to 'contemptuous' in this list. 'Sympathetic' means showing compassion, 'exhausted' means very tired, and 'insensitive' means lacking empathy. These options do not convey the same meaning as 'contemptuous'.