世界最大的平原和高原都位于（  ）

增加：在缺词处加一个漏词符号（∧），并在其下面写出该加的词。

删除：把多余的词用斜线（\）划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1). 每处错误及其修改均仅限一词；

2). 只允许修改10处，多者（从第11处起）不计分。

    I asked Jack, a friend of mine, what has happened to him that night. He said that he had just got into bed on about half past eleven when the floor began to shake under him. The bed was also started shaking. He jumped out of his bed rapid and wanted to turn the light on. But the floor was shaking such violently that he could hardly reach the lamp. It seemed to take him long time to get to it and turned it on. Then he went to look out of the window. He saw that the houses on the other side of the street was also shaking. Then he knew that was happening — an earthquake! He quickly put on his clothes and ran out into the street to waiting until it was safe to go back inside.

①当时使用蒸汽机的都是英国人     ②以蒸汽为动力的机器都是英国发明的

③当时的英国已广泛使用蒸汽机     ④蒸汽机的出现是英国工业革命的象征

下列图形是电与磁中的几个实验，能反映电动机工作原理的是（　　）

城市生活垃圾的成分构成具有地域差异，我国南方的不可回收无机物（煤灰等）远低于北方，而不可回收有机物（菜叶等）远高于北方。导致这种差异的主要自然因素是（   ）