1. I find that it is difficult to learn English well, so I mu.st study harder.

    I find ______difficult_______ _____English well,so I must study harder.

2. He didn't get married until he was in his thirties.

    It was______ _______he was in his thirties ______he got married.

3. We started early so that we could arrive there before 8 o'clock.

    We started early_______ ______ _______arrivethere before 8 o'clock.

4. They hurried up because it was getting dark.

     ________ __________ because it was getting dark _______ they hurried up.

5. It's mad of you to go there alone in such bad weather.

    ________ ________ ________you to go there alone in  such bad weather.

如图，物体A与B用跨过滑轮的细绳相连，已知物体B的重力为80N，地面对B的支持力为60N，连接物体B的细绳与水平地面夹角为30°，所有物体保持静止。

小题1:计算物体A的重力

小题2:计算地面对物体B的摩擦力

小题3:若物体B在水平向右外力作用下匀速向右运动过程中，请判断水平外力及地面对物体B摩擦力的变化情况。（设物体A未升至滑轮处）