VOA慢速英语:国家公园平衡对电话服务的需求

cliff -n. a high, steep surface of rock, earth, or ice

maintain -v. to continue having or doing (something)

tourist -n. a person who travels to a place for pleasure

access -n. a way of being able to use or get something

survey -n. an activity in which many people are asked a question or a series of questions in order to gather information about what most people do or think about something