[单选题]在采煤机内喷雾不能正常使用时，外喷雾压力不得小于（）Mp。
A.1.5
B.2
C.4

When we think of green buildings, we tend to think of new ones—the kind of high-tech, solar-paneled masterpieces that make the covers of architecture magazines. But the U.S. has more than 100 million existing homes, and it would be (1) wasteful to tear them all down and (2) them with greener versions. An enormous amount of energy and resources went into the construction of those houses. And it would take an average of 65 years for the (3) carbon emissions from a new energy-efficient home to make up for the resources lost by destroying an old one. So in the broadest (4) , the greenest home is the one that has already been built. But at the same time, nearly half of U.S. carbon emissions come from heating, cooling and (5) our homes, offices and other buildings. "You can’t deal with climate change without dealing with existing buildings," says Richard Moe, the president of the National Trust.
With some (6)