单项选择题
Questions 28 to 30 are based on the following news. At the end of the news item, you will be given 15 seconds to answer the questions. Now, listen to the news.
What is the purpose of the national survey（）
A．To collect data on sources of pollution.
B．To identify pollution in rivers and lakes.
C．To help control environmental pollution.
D．To help control industrial wastes.