What will happen if you don't arrive soon?

The answer "We will leave without you" is accurate because it communicates a specific action that is contingent on the timing of the person's arrival. It indicates a direct consequence: if the person does not arrive soon, the group will not wait and will proceed without them. This highlights a sense of urgency and the expectations of the group regarding departure.

The other choices, while they may also be plausible consequences of not arriving soon, do not capture the explicit action taken by others. For instance, stating "You will miss the train" suggests an outcome for the individual but does not imply any action from others. "You will be late" conveys that the person will not meet the expected timeframe, but similarly, it does not reflect an action on the part of the group. Lastly, "We will wait indefinitely" suggests that the group intends to wait, which contradicts the expectation of departing soon if the person is late. The selected answer emphasizes a proactive decision from the group, making it the most fitting response in the given context.