有问必答

李顺发

It， that， one用法相比较，有哪些异同？

答：1. it和that都可用来代替物质名词和抽象名词，而one则不能。这时it指同一事物，而that只能指同类事物。如：

①There is air all around us， though we cant see it.

②His attitude to us is that of a comrade.

③Your question is one of great importance.

以上句①it替代同一air。句②that替代attitude.His attitude与the attitude of a comrade是同一类的。句③one替代可数名词question.

2. it， that， one都可用于代替可数名词。that和one只是代表上文提到的某一个名词，不一定代表同一事物。其中one表示泛指，代替a/an+名词（可数名词）；that表示特指，代替the+名词；it也表示特指，但它代表上文提到的名词时，是指同一个事物。

①—Do you need my pencil ？

—No， thanks. I have got one myself.

②—Where is my book？

—I have lost it.

句①中的one不是上句提到的“我的pencil”，而是另外一支，表示泛指；句②中的it就是指上句提到的“我的那本书”。

3. one前面可以有冠词、代词、形容词修饰，后面可以有介词短语、定语从句修饰，而it和that前面则不能。one的复数形式为ones.

I dont want a new car. I want a second-hand one.

The book is one about English study.

Our era is one in which a great number of heroes emerge.

—Which book would you like—this one or that one？

—Either one is fine.

Here are two pens. Which one do you prefer ？

—This is very beautiful.

—Yes， at least it is no worse than the one I bought last week.

Modern farms are larger than old-time ones.

In Britain the villages are becoming small towns and the small towns large ones.

4. it和that可用来代替前面整个句子的意思，而one则不能。

I would like to give him a hand. It is my duty.

During the next ten years we both worked night and day. That is why you see this old woman before you now.

5. 在比较状语从句中，一般用that代替不可数名词。若是特指的单数可数名词，用that one；若是特指的复数名词，则用those代替。

The population of China is much larger than that of Japan.

No bread eaten by man is so sweet as that earned by his own labour.

We like this computer better than that one.

The people in this place are more hardworking than those in that place.

“be+to do”结构有哪些用法？

答：1. 表示按计划或安排将要做的事情。如：

The train for Wuhan is to start at 10：20. 去武汉的火车10点20分开。

We are to begin the work next month. 我们计划下个月开始这项工作

She is to be seen in the lab on Monday. 星期一你准会在实验室见到她。

这一结构也可用于表示过去曾经计划要做的事。如果这种事没有发生，可以用动词不定式的完成式。如：

She was to have summer holidays in Dalian last year. 去年她曾打算去大连度暑假。

I was to have started work last week， but I changed my mind. 我本该上星期开始工作，但我改变了主意。

2. 表示命令指示。如：

Mother says you are to wait here till she comes. 妈妈要你在这儿一直等到她来。

You are not to smoke. 不准吸烟。

The room is to be locked. 这房间要上锁。