They arrived ___ time to catch the last train.

• A. On
• B. In
• C. At
• D. By

Answer: (A)

The main idea here is how we express punctuality relative to a schedule. The phrase on time means arriving exactly when you’re supposed to, being punctual. In this sentence, arriving on time lets them catch the last train because they’re not late for its departure. If you used in time, the emphasis would shift to having enough time before something happens, which changes the nuance to “before it’s too late,” rather than simply being at the scheduled moment. The other options aren’t natural for describing punctual arrival to catch a specific train; they don’t express arriving at the exact scheduled moment. So the natural, idiomatic choice is to say they arrived on time.