A few years ago, I was eating dinner with my children before we went to a museum. We were talking ____ (愉快地) when a man walked up to me and asked if I had a ____dollars to give him. I replied that I didn't even have one coin on me. Of course, my kids stood up and said: “Yes, you do, mommy.” I was a little embarrassed because I felt as if they____(抓住)me not telling the truth. Normally, I don't carry lots of money in my ____, instead, I pay with my bank card everywhere I go.

    So I told the man I could u____my bank card to buy him something to eat. His disappointing____(表情) quickly changed into a smile. Then I went to get him some kinds of food. He thanked me when I h____him a bag of food. After he left. I had a talk____my children: "Usually, I don't always like giving money to everyone who asks for it. H____, I am not against meeting the needs of others as I____as I have it. "I felt good knowing that the man had a nice meal that evening.

有一个四位数，这个数的最高位是千位．

有位同学按如下步骤做了“绿叶在光下制造淀粉”的实验，结果发现叶片的所有部分都变成蓝色，请你帮他诊断一下是哪个步骤操作不当造成的①把实验植物先置于黑暗处一昼夜②用不透光的黑纸片将所选叶片的上表面的一部分遮盖起来③将植物移到光下照射三个小时④剪下叶片，放入酒精中隔水加热⑤用清水冲洗叶片后滴上碘液（　　）

如右图甲所示，一辆遥控小车静止在水平面上，现用遥控器启动小车，使它从静止开始运动，小车运动的速度与时间关系的v﹣t图象如图乙所示．已知小车的质量m=2kg，小车与水平面间的动摩擦因数u=0.2，重力加速度，g取10m/s²则下列说法中正确的是（　　）

黄河水土流失最严重的河段是(　　)