By 1999, after the clean water act had been passed in 1970, the percentage of u. s. surface waters safe for fishing and swimming had increased from 36 percent to

The correct answer is 60 percent.

Explanation:

The Clean Water Act refers to a federal law of United States, which observes the release of contaminants into the surface waters of the country, comprising rivers, lakes, wetlands, streams, and coastal areas. Approximately 30 years after passing of the Clean Water Act in the United States, the percentage of surface water, that is, regarded safe for swimming and fishing had enhanced from 36 percent to 60 percent, which is approximate twice the original value. Some kind of policies and programs were implemented as part of the act.

b tumor cells have a cell wall instead of a membrane

explanation:

tumor cells different from normal cells because tumor cells have a cell wall instead of a membrane.