Select the meaning of the underlined word in the sentence.

Providing immunizations to the indigent population falls under the aegis of the public health department.

In this context, the word "etiology" refers to the cause or origin of something, in particular, the cause of the flu epidemic of 1918.

It implies the study or understanding of the underlying factors or reasons that led to the occurrence of the epidemic. The options "transmission," "mortality rate," and "pathology" do not accurately reflect the meaning of "etiology" as it is used in this sentence.

In this context, "labile" refers to the patient's condition being unstable or prone to rapid and unpredictable changes.

The sentence suggests that the patient's health or medical status is fluctuating, and as a result, the nurses were instructed to closely monitor him. The word "labile" is often used in a medical context to describe a condition or state that is variable and can change quickly. Therefore, option B, "Rapidly changing," is the correct answer.

Stop

In the given sentence, "cease" means that the rain will come to an end or stop. It suggests that the rain will no longer be falling after sundown. Therefore, option D, "Stop," is the correct answer.

The verb "assemble" means to bring together or gather in one place or group. It implies the act of collecting or uniting individuals or things in a coordinated manner. Therefore, "assemble" is the correct word that describes the action of gathering together. The options "appearance," "assembly," and "semblance" do not convey the same meaning as "to gather together."