放煤时，工作人员应站在本架的（）上。
A.前柱
B.四连杆
C.拉后溜顶
D.脚踏板
参考答案：D
The reason he was absent from class was his mother fell ill this morning.
A．for; that
B．why; that
C．for; because
D．why; because
一太阳能热水器水箱内装有质量为80kg的水，经太阳晒2h后，温度从20℃升高到50℃所吸收的热量是______J，这是用______的方式增加了水的内能．
