499c0138     王怡涵 

1. The first kind is a physical border. Physical borders between countries can be rivers or mountains. (next sentence )

2. They were not physical features, such as rivers or mountains.

3. Government officials at the borders check, that is, take a careful look at, everyone who enters.

4. In many countries, there is a tax on things that enter the country. A tax is money that you must pay to the government. (next sentence )

5. The ocean and the land under the ocean have many natural resources, such as fish and oil.