题目

It happened to me recently. I was telling someone how much I had enjoyed reading Barack Obama’s Dreams From My Father and how it had changed my views of our President. A friend I was talking to agreed with me that it was ,in his words, “a brilliantly（精彩地）written book”. However, he then went on to talk about Mr Obama in a way which suggested he had no idea of his background at all. I sensed that I was talking to a book liar. And it seems that my friend is not the only one. Approximately two thirds of people have lied about reading a book which they haven’t. In the World一头质量为6×103kg的大象，每只脚掌的面积，为600cm2，它的重力为    N，它四脚着地时对地面的压强为    Pa．若大象抬起一条腿，如图所示，它对地面的压强（选填“变大”“变小”“不变”）    ．（g取10N/公斤）