Travel is a very good activity. When traveling, you can relax小题1:  ,forget your tiredness or troubles, and have the energy to take on the new tasks waiting for you.

But sometimes traveling is 小题2:   an enjoyable thing. For example, the weather can be changeable, If you climb a mountain, it may rain suddenly. You may be caught小题3:   the rain and may catch a cold. The worst thing is that you may have your money stolen 小题4:   you may have an injury. All these terrible things are 小题5:  can happen to you .

Therefore, when you are going on a trip, you 小题6:   make a good preparation. Firstly, you must have clear information about the weather. Secondly, you should choose小题7:___good companion so that you can help each other. Thirdly, you must be careful enough and try to avoid accidents. 小题8:  you do this, you will surely enjoy your travel.

如图所示，O为轻质杠杆AB的支点，杠杆上刻度均匀，在距支点10厘米的B处挂有600牛的重物，要使杠杆平衡，需要在A处至少加__________牛的力，且方向为__________。