What word completes the man's explanation for feeling stressed?

The correct choice is "Since," which effectively establishes a cause-and-effect relationship in the context of the man's explanation for feeling stressed. Using "Since" indicates that the following statement will detail a reason or circumstance that has been ongoing, contributing to the man's stress levels.

In spoken or written communication, "Since" often introduces a time frame or justification, suggesting that the stress has been a result of a situation that began in the past and continues into the present. This choice helps convey that there is a direct link between the man's feelings of stress and specific events or changes that have occurred over time.

The other options do not appropriately convey the same meaning. For instance, "Until" implies a time restriction or condition that has not yet been fulfilled, which would not accurately reflect the man's ongoing experience of stress. "After" suggests a sequence that would not effectively connect his stress to present circumstances since it implies that a particular event must have already happened. "During" indicates that the stress is tied to a certain period but does not clarify the reason behind the stress comprehensively, lacking the causal aspect that "Since" provides.