[单项选择]

Lisa was running late. Lisa, 25, had a lot to do at work, plus visitors on the way : her parents were coming in for Thanksgiving from her hometown. But as she hurried down the subway stairs, she started to feel uncomfortably warn. By the time she got to the platform, Lisa felt weak and tired—maybe it hadn’t been a good idea to give blood the night before, she thought. She rested herself against a post close to the tracks. Several yards away, Frank, 43, and his girlfriend, Jennifer, found a spot close to where the front of the train would stop. They were deep in discussion about a house they were thinking of buying. But when he heard the scream, followed by someone yelling, "Oh, my God, she fell in!" Frank didn’t hesitate. He jumped down to the tracks and ran some 40 feet toward the body lying on the rails. "No! Not you!" his girlfriend screamed after him. She was right to be alarmed. By the time Frank reached Lisa, he could feel the tracks sh
A. Because they would miss their train.
B. Because he didn’t see the train coming.
C. Because she was sure Lisa was hard to lift.
D. Because she was afraid the train would kill him.