风道阻力
参考答案：包括冷风道、空气预热器、热风道和燃烧设备的阻力。
—Children often have fun swimming _____. Do you often go there?
—Yes. My parents usully talk me there.[ ]
A. at the pool
B. in the library
C. at the airport
安全技术措施制的重点哪些？
