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It was a sunny day last Sunday. Liu Mei went shopping with her mother. On her way to the shop, they met (遇见) an old woman. The old woman wanted to see her husband (丈夫). He had a flu and was ill in hospital. But she did not know the way to the hospital. Liu Mei asked a policeman. He told (告诉) her to take the No. 11 bus. Liu Mei went with the old woman to the hospital and her mother went shopping by herself. Forty minutes later, the old woman saw her husband. Liu Mei left the hospital and went to the bookstore. She did not wait for their thanks.
处放一点电荷q，则它所受静电力的大小为
