Final answer:
The implied main idea of the passage about Justin is not provided; however, it would be an idea that the author wants the reader to understand based on the context of Justin's situation, which is not directly stated.
Step-by-step explanation:
The implied main idea of a passage is what the author wants the reader to understand without stating it directly. In the case of the passage about Justin, we have to infer the main idea based on the provided details. If Justin is hurrying through the city, it implies a sense of urgency, but we don't know the cause without more context. If the passage indicates he is rushing but then later mentions he missed his train, the implied main idea might lean towards option (a); however, this is not definitive without further context. Similarly, if there is text that suggests Justin was kept at school, which made him late, option (b) could be inferred. Option (c) is more of a factual statement than an implied main idea, and option (d) could be part of the story, but it is not enough to be the main idea on its own unless the passage focuses on the implications of the train leaving. The answer would largely depend on the actual content and details of the passage.