Loudspeakers were fixed in the hall so that everyone______an

a.ought to have 近似should,但含有义务责任所以不选
b.must have 语气强硬 必须
c.may have 改成might 就是标答
d.should have 只有D 了
2006专四考题,真的吗?怪题
loudspeakers were fixed in the hall so that everyone might have an opportunity to hear the speech.
loudspeakers were fixed in the hall because everyone should have an opportunity to hear the speech.
got it?

D =could have 表示有能力,有条件
A 应该可以,扩音器修好了不能为了应该可以.

第一个是因为你没弄懂这个句子的意思.后一句的意思是：以便每一个人________一个机会去听到演讲.
而a.理应去有 b .必须有 C.可以有 D.应该有.
第二个.在这个地方,should是表示演讲者的目的的,所以意思是：会,可以.,他讲话慢的以便每个人可以理解他说了些什么.（目的让别人听懂.）
(表示目的)会,可以 ,而C.may不具有目的性.
例如：He stood away so that we should enter the room first.
他让开一步,让我们先进屋.
第三个.因为need not to do .不需要去做某事(但是已经做了.）而needn't do 是不需要做（还没做的事）

虚拟语气不仅用于条件从句,下面的从句也需要用虚拟语气：
1.表示个人意愿（如建议、命令、要求、主张等）的名词从句——动词要用 should do 或者省略 should 直接用动词原形 do,如：
1）宾语从句：I suggested that he (should) leave for the city tomorrow.
2）主语从句：
it is essential that he (should) do it right away.他有必要马上就做这件事.
It is important that we (should) consider such a matter before everything.优先考虑这种问题是紧要的.
It is suggested that he (should) leave for the city tomorrow.
2）so that / in order that 引导的的目的状语从句,谓语动词必须含有can/could、may/might、should 等情态动词.如本题：
loudspeakers were fixed in the hall so that everyone should have an opportunity to hear
the speach.
选项都是情态动词但是意思各不相同——
A ought to ：用于表示义务或责任上的应该,用在本题不合题意.
B must have：表示道德良心、法律或者习惯所要求的应该,不合题意.
C may have：原题主句用的是过去时态,只有 might have 方可以在此处表示有可能的意思,因此是时态错误.
D should have 表示期望到的可能性,用在本句中意思是“大厅里都安装过扩音器,以便期望大家都有机会听到讲演”.

两个扬声器相隔一米,辐射相同的声压水平.监听器是在前面的一位发言者直接在两米的线,垂直线连接两个扬声器,见图2.前两个是什么
在这破坏性的干扰频率发生?什么时候第一次体验建设性干涉监听,在非常低的频率比其他?
插一句,这到底是物理还是外语