The subject 'jumped off the train' is event # 1, and the 'train moving' is event # 2. When there are two events in a sentence, we must decide which event is the longer, ongoing one and which the interrupting one. Here, the man's 'jumping' is the action that is shorter and interrupting the event. Since it is in the simple past tense, we must use the past continuous tense to describe the ongoing event: the train's running. Hence, the right answer is option A) was running.