换热器的作用是使两种温度不同的介质进行热量交换，达到（）的目的。
A.加热或冷却
B.加热
C.冷却
D.升温
参考答案：A, B
The king is said to _______ by the spider weaving its web in the cave where he was hiding and defeated his enemy at last.
A．be encouraged
B．being encouraged
C．have been encouraged
D．have encouraged
青春期是人生的“花样年华”，其发育的显著特征是（ ）
A．身高和体重迅速增长
B．出现第二性征
C．心、肺功能大大增强
D．性发育与性成熟
