a powerful small boat designed to pull or push larger ships
造句
用作名詞(n.)
For example, permits could be issued to travel through locks at specified times, and those permits could be traded among towboat captains. 比如，可以通過許可證的發放將船閘通行限定在指定時間內，而且許可證也可以在拖船船長之間進行交易。