单项选择题 21（）

单项选择题 Why is insulation required in new houses

单项选择题 What’ s the talk mainly about

填空题 What characteristics can be of a flood

单项选择题 What do we learn about the use of solar energy in the USA

单项选择题 What is the main topic of the lecture

填空题 What does "runoff" mean

填空题 Noise constitutes a real and present danger to ______ .

填空题 Noise is America’ s most widespread ______ .