We won’t start the work until all the preparations ________.

A. are being made    B. will be made      C. have been made D. had been made

答案为C。请问这种情况为什么不用现在时呢？A 可以么？现在进行时算作一般现在时，这里现在完成时是什么用法，是发生了的事情还是将要发生的呢？

回答如下：

以上从句使用现在完成时态还具有以下含义

在时间或条件状语从句中，当表示将来完成时的意义时，要用现在完成时来代替将来完成时。 (从句所使用连词有 if, when, until, by the time)

We’ll start at 5 o’clock if it has stopped raining by then. 

I shall go to see you whenI have finished my homework. 

We won't start  the work until all the preparations have been made.

回答如下：

以上4个答案解析如下：

A:re being made 为现在进行时的被动语态 意思为“现在正在被做”

B:will be made 为一般将来时被动语态，意思为“将要被做”

C:have been made 为现在完成时被动语态，意思为“某个动作已经被做且对现在造成影响和产生某种结果，根据句子意思 ，产生影响和结果就是我们开始这项工作，正好符合句子意思表达，因此C为正确答案。

D:had been made 为过去完成时被动语态度，意思为“在过去某一时间之前已经被做了” 需要有个过去时间点作为参照。

回答如下：

We won't start the work until all  the preparations have been made.

直到作好了所有准备，我们才开始这项工作。

首先可以肯定正确答案为C.原因如下：

(1)until 引导时间状语从句用现在完成时态表示语境是在从句动作已经结束完成后，主句动作才发生的。即从句所表示时间为主句动作开始时间。

结构为：A +will not do sth until B have/has done sth

结构为：Don't do sth until A has/have done sth(在A做某事情之前，不要做某事情）

意思：A直到B已做了某事情才会做某事情

意思：在B做某事情之前，A不会做某事情

Don’t get off the bus until it has stopped. 

车停稳了以后再下车。

She won't go home until she has finished all her work.

她直到完成她所有工作才回家。

关于连词until引导的从句中谓语动词的时态。 

A:主句的谓语动词为一般现在时或一般将来时时或者是祈使句形式， until从句中的谓语动词为现在完成时，用来强调从句谓语动词表示的动作发生在主句谓语动词表示的动作之前。 

I won’t go to bed until I have finished my homework. 

我要完成作业才睡觉。 

B:主句中的谓语动词为一般过去时时，从句中的谓语动词为过去完成时，用来强调从句谓语动词的动作发生在主句谓语动词表示的动作之前。

Li Lei didn’t come until the film had begun.

直到电影开演，李雷才来。

c答案中可以加上will 吧？如果有此答案正确么？二者有何区别？另如果有答案are made 正确么？谢谢

继续跟踪回答如下

C 答案不可以加will ,will have been made 属于过将来完成时态，表示在将来某一时间完成结束的动作。不符合句子意思和语境。

将来完成时态表示以下2种基本含义：

A:表示将来某一时时间之前或在从句动作发生时就已完成的动作：

I  will have  have  finished  the work  by  next Friday.

The work will  have been finished by me by next Friday.

到下个星期五时，我就已经完成了这项工作了。

I will finish my homework  by the time you come back.

当你回答的 时候，我就已经完成了我的家庭作业了。

B:表示一个持续到将来某时或动作发生时已完成的动作，这样用时必须有一个表示未来时间的状语：

By next Sunday he will have lived  in Beijing for 20 years.

到下个星期天，他就将在这里住了有20年了。

By 2030,we will have discovered a treatment that can cure all kinds of cancer.

By the end of the century , we will have produced new types of clothes.

We will have learned 24 units by he end of this term.

They will have been married for 20 years by then.

I will have finished all the work by the time you come back this evening.

Before you get home, I will have cleaned the house from top to bottom.

When winter comes, the animals will have savedenough food.

将来完成时态常用结构为

(1)A will have done sth before B do/does sth

(2)A will have done sth by the time B do/does sth

(3) A will have done sth by+表示将来的时间状语

(4) A will have done sth when B do/does sth 

(备注以上1/2/4从句谓语时态都为 一般现在时态，主句谓语时态为将来完成时态)

最后总结如下：

(1)主句用一般将来完成时态，时间状语从句用一般现在时态代替一般将来时态。

I will have finished all the work by the time you come back this evening.

Before you get home, I will have cleaned the house from top to bottom.

When winter comes, the animals will have saved enough food.

(2)主句用一般将来时态，时间状语从句用现在完成时态代替一般将来完成时态。

We will start at 5 o’clock if it has stopped raining by then. 

I will go to see you when I have finished my homework. 

We won't start  the work until all the preparations have been made.

( 备注:以上从句所使用连词通常为 if, when, until, by the time。)