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(guò)許可證的發(fā)放將船閘通行限定在指定時(shí)間內(nèi)，而且許可證也可以在拖船船長(zhǎng)之間進(jìn)行交易。