找出下列句子的一处语法错误：

　　When a serious pollution problem has been created by a factory, which representing a health threat to citizens, it is also advisable to turn to the government for help.

　　♜ 适用考题：

　　Most people can solve important problems in their lives by themselves or with the help of their families; help from the government is often unnecessary. (2012.1.8)

　　答案：

　　When a serious pollution problem has been created by a factory, which represents a health threat to citizens, it is also advisable to turn to the government for help.