What phrase suggests that Jack has been going to the gym?

The phrase "He's been going" indicates that Jack has been regularly attending the gym over a certain period of time. The use of the present perfect continuous tense ("has been going") suggests that his gym attendance is ongoing and was initiated in the past, continuing up to the present moment. This phrase emphasizes the duration and continuity of the action, which aligns well with the idea of regularly going to the gym.

In contrast, the other options denote different aspects of time and frequency. "He went" refers to a completed action that took place in the past without indicating a connection to the present. "He is going" describes a current action but does not imply that this action has occurred repeatedly over time. Lastly, "He goes" signifies a habitual action but lacks the context of ongoing activity suggesting recent or continued attendance. Thus, "He's been going" effectively captures the idea of Jack's ongoing commitment to going to the gym.