a crowded train的用法和样例：
- I'd prefer to go there on a crowded train rather than on an airplane.
- I had been sitting in a crowded train for more than four hours. When I tried to get out,I had pins and needles in my leg.
- He headed a crowd off from the wrong exit.
- A crowd gathered at the scene of the fire.
- He did the deed in view of a crowd of people.