Question

新概念英语中的几个问题

新概念英语第二册的一篇文章，大家请看我在其中的几个句子钱的编号。 A pilot noticed a balloon which seemed to① be making for a Royal Air Force Station nearby. He informed the station at once, but no one there was able to explain the mystery. The officer in the control tower was very angry when he heard the news, because balloons can be a great danger to aircraft. He said that someone ②might be spying on the station and the pilot was ordered to keep track of the strange object. The pilot managed to circle the balloon for some time. He could make out three men in a basket under it and one of them was holding a pair of binoculars. When the balloon ③was over the station, the pilot saw one of the men taking photographs. Soon afterwards, the balloon began to descend and it landed near an airfield. The police were called in, but they could not arrest anyone, for the basket contained two Members of Parliament and the Commanding Officer of the station! As the Commanding Officer explained later, one half of the station did not know what the other half was doing

问题：①处为什么加be?而不是was
②处为什么用might而不是may?spy为什么加ing?
③处was over 是什么时态? 为什么不When the balloon over the station？为什么加was？
谢谢各位了

Answer 1

①seemed to be doing 好像在做某事 was doing 在做某事 因为意思不一样
②时态要求 主句谓语是said 所以间接引语用might而不是may
spy加ing是现在分词 与助动词be 构成进行时 spy是动词
③was over 是状语从句中的 谓语 over是介词 与后面的 名词一起 构成介词短语
作系动词was的 表语 是一般过去时
因为When the balloon over the station是从句 没有谓语动词 介词短语不能作谓语 所以
必须加was