题目

完形填空 When I was in middle school, I got mad at my parents because they would never give anything to the homeless that passed by us. On a family vacation in Washington D.C., there was a 1 man down the street. My family2 with our eyes at our feet. On our final day in the city, when my 3 went for an evening walk, I ran out of our hotel room 4 and ran down the street to the homeless man. He looked at me with curiosity, surely not5 anything from a middle school girl. I asked him what he would have for 6. He replied he would have hamburgers. I ran into the grocery store down the block and 7 如图所示，M、N是平行板电容器的两个极板，R0为定值电阻，R1、R2为可调电阻，用绝缘细线将质量为m、带正电的小球悬于电容器内部．闭合电键S，小球静止时受到悬线的拉力为F．调节R1、R2，关于F的大小判断正确的是（ ）A．保持R1不变，缓慢增大R2时，F将变大B．保持R1不变，缓慢增大R2时，F将变小C．保持R2不变，缓慢增大R1时，F将变大D．保持R2不变，缓慢增大R1时，F将变小