What is the meaning of acarpous?

The term "acarpous" specifically refers to something that is no longer able to produce fruit or seeds, indicating a state of infertility or a lack of reproductive capability. In a broader sense, it can also imply that something has become worn out or exhausted, particularly in the context of its productive capacity.

The other choices, while related to concepts of lack of productivity or effectiveness, do not capture the biological nuance present in "acarpous." For instance, while "futile," "ineffective," and "unproductive" convey a general sense of not achieving desired outcomes, they do not specifically address the biological connotation of being worn out or no longer fertile, which is crucial to understanding the term accurately. Thus, the choice that aligns best with the meaning of "acarpous" is the one that indicates a loss of fertility and a state of having become exhausted in terms of reproductive ability.