One night Mr. Lee was driving his wife home from work. She was a staff nurse in a hospital. It was almost midnight and she was quite tired out. She soon fell asleep. Mr Lee looked at her and smiled. Mr. Lee was a cautious and experienced driver. He knew it was safer to drive slowly on a dark night. After some time he noticed a car following him. It was traveling very fast. Suddenly it overtook his car. The driver of the car was in a hurry. He did not see the approaching lorry . To avoid hitting it, he swerved his car. It skidded off the road and hit a big tree. The driver and his passenger were injured. They were badly cut by glass splinter from the broken windscreen. Mr. Lee quickly stopped his car by the side of the road. His wife got out of the car to help the injured men. The lorry driver also stopped to lend a helping hand. Mr. Lee immediately drove off to telephone the police. About twenty- five minutes later, a police car and an ambulance arrived. The injured men were carried into the ambulance and taken to hospital. The policemen took down details of the accident. Mr. Lee and the lorry driver told them all that they could remember. The policemen thanked them for their help. Mr. and Mrs. Lee then got into their car and continued their journey home. Mrs. Lee fell asleep in the car because  _  .
she was very tired her husband was driving very slowly it was too late both A and C