I always wondered how people would react if I tried to approach a total stranger for help in a busy place like a street corner or a mall. I have always 1 a stranger who tried to catch my2 in a busy place.

    Yesterday I was in a busy shopping mall buying a large piece of luggage because I just had the 3 to do it after many days of planning. After the 4 I picked up my phone from my pocket to call my driver waiting in the parking lot but my phone was 5.

    Then I requested the shop assistant who had 6 sold me the merchandise (which was not cheap), if she could ring my driver for me. She 7 that it was the shop policy that they cannot use 8 while working in the shop.

    After I got out of the shop onto the busy street, I 9 a young mother with her two kids to make the same 10As soon as I said “Excuse me, madam!” she grabbed her kids and ran. I 11 a kidnapper(绑匪).

    I stood there wondering how many times I had 12 to strangers like the young13 I stood there in the 14 street with people rushing by, looking at their faces to see if there was a sign of 15 on their face.

I saw a man pretty shabbily dressed compared to me who 16 to notice me. I just stopped him and made my request. He17called my driver and waited till my car came to make sure I was picked up, turned around 18 I could thank him adequately and was gone.

    I was 19 by kindness and hope I will do20 to strangers who try to catch my attention from now on.

造成黄土高原水土流失的土质原因是（　　）

如图所示，质量为160Kg、底面积为0.25m²的物体平放在深井底．已知物体的密度为1.6×10³Kg/m³，g=10N/Kg．则：

（1）物体对井底的压强是多少？

（2）若井深10米，要将此物体拉到井口之上，至少需要做多少功？

（3）若改用水将井灌满，则至少用多大的力才能把物体提起？