1. Its citizens breathe air that is dangerously polluted.
    它的公民们呼吸着对他们有很大危害的、被污染了的空气。

2. Now, 500 years later, excessive fishing has reduced the number of fish to dangerously low levels.
    500年以后的今天，过度捕捞已使鱼的数量减少到危险的程度。