什么是对流受热面？
参考答案：
安装在炉膛出口以后，以吸收烟气对流热量为主的受热面叫做对流受热面。
His grandfather died ____ the wound that the enemy soldier had given him .and then his grand-
mother died ____ hungry and cold.
A．from,of
B．of,from
C．from,from
D．of.of
不同频率的正弦量之间（）存在相位差的概念。
