适合砌筑处于潮湿环境下的砌体是( )。
A．石灰膏 B．石灰砂浆C．水泥砂浆 D．混合砂浆
参考答案：C
用所给词的适当形式填空。
1. Bill Gates became ________ (interest) in software when he was only 13.
2. Bill Gates is the man who is taking the ________ (person) computer into everyone's home.
3. Mrs. Wang is very nice. She is ________ (friend) to us every student.
4. Grace is very sure of ________ (she).
5. My father plans ________ (retire) at the age of 50.
（1）物块随传送带一起向上做匀速直线运到，在图1画出物体受到的摩擦力．
（2）一人站在电梯上随电梯一起匀速上升，如图2所示，画出人的受力示意图．
（3）如图3所示，AOB为一机械设备的简化示意图，我们可以把它看成杠杆（自重不计），已知AO=2OB．固定O点，使OB 处于水平位置，此时B端挂一重为40N的物体，要使杠杆不发生转动，至少需在A端施加F=______N的力，在图上画出此时力F的方向．
ng the ________ (person) computer into everyone's home. 