Which of the following best describes the action of "plummet"?

The action of "plummet" is best described by the phrase "to drop sharply." This term conveys a sudden and often significant decline or fall, typically in a vertical direction. For example, if the stock market were to plummet, it would mean that the prices of stocks are dropping rapidly and significantly, often causing concern among investors.

The other choices, while they describe different actions, do not capture the essence of "plummet." For instance, the idea of weeding out unwanted things refers to a process of selection or removal rather than a fall. Bringing about something abruptly suggests initiating an action quickly, which does not align with the concept of dropping or falling. The notion of transmitting or spreading pertains to movement or distribution, again diverging from the straightforward action of falling sharply that "plummet" signifies. Therefore, "to drop sharply" is the most accurate description of "plummet."