What will happen if they miss the early train?

The correct answer highlights the implication of missing the early train, specifically that it would lead to the consequences associated with not having lunch. The phrase "it will mean missing lunch" directly connects the action of missing the early train with the resultant outcome, clearly indicating a cause-and-effect relationship. This construction emphasizes that the missing train is a significant factor that directly precludes the possibility of having lunch, thereby conveying the intended message with clarity.

The alternatives do not effectively capture this direct connection as well. For example, saying "it will result in missing lunch" might imply a more complex chain of events rather than a straightforward consequence, which makes it slightly less direct in communicating the relationship. Similarly, "it will cause missing lunch" suggests a more forceful action and may come across as less natural in everyday language. Lastly, "it will affect lunch" is vague and does not clearly define how the lunch will be impacted. It lacks the specificity of what exactly will happen if the train is missed. Overall, the chosen response is the most concise and clear way to articulate the intended consequence of missing the train.