Topic: Idioms & Phrases,

Best Answer Explained in Below-:

The phrase "at my wits' end" originates from the idea of reaching the limit of one's mental or emotional resources. When someone says they are "at their wits' end," it signifies an overwhelming feeling of frustration, confusion, or desperation. It implies that they have exhausted all possible solutions or thoughts regarding a particular problem and are unable to find a way forward.

Given this understanding, option B—"cannot figure out"—is the correct choice. It captures the essence of the expression, highlighting a state of mental blockage where solutions seem elusive and clarity is lacking. The other options do not fit the context; for example, option A ("totally understand") contradicts the meaning, and option C ("witness the end") does not relate to mental strain or confusion. Therefore, identifying that one is "at their wits' end" indicates they are grappling with a problem they are unable to solve, aligning perfectly with the concept of being unable to figure things out.