汽轮发电机组的循环热效率
参考答案：
每千克蒸汽在汽轮机中的理想焓降与每千克蒸汽在锅炉中所吸收的热量之比称为汽轮发电机组的循环热效率。
Look at the pride on Tom's face. He _____ to have been praised by the manager just now. [ ]
A. seemed
B. seems
C. had seemed
D. is seeming
B．摩擦力一定阻碍物体的运动，所以它总是阻力
C．摩擦力既可作为阻力，有时也能当作动力
D．我们常用增大压力的办法来增大摩擦力
