正因为她无法养家才同意做家仆。
It was because she can't support her family that
she agreed to be a domestic.
1.为什么用现在时can't而不用过去式could't；这个句子时态对吗？
2.详细分析这个句子、主要是时态、结构、语法~

【1】我认为本句时态不正确,can这里表示 主语 的能力，且整个句子时态为过去式，所以要用couldn't.
It was because she ccouldn't support her family that she agreed to be a domestic.
【2】本句话为It is/was ... that/that... 强调句型。
此处，强调的是原因状语 because she can't support her family. 详细用法参见后面附录


【can做表示能力，会】can表示主语的能力。能, 会。如：
Can you play the piano? 你会弹钢琴吗?
It was so dark that I could see (=I saw) nothing.
天太黑了，我啥也看不见。
The hall can seat 1,000 people. 这个大厅能坐1 000人。
could表示主语的能力，为can的过去时形式，如：
They said they could swim. 他们说他们会游泳。


【附录】强调句型的用法

在英语中，我们常用It is／was… who/that结构来突出强调句子的某一成分(一般是句子中主语，宾语或状语)。在这个句型中，it没有词汇意义，只是引出被强调的成分。如果被强调的成分是表示人的词，用who或that来连接都可以。如果是其它成分，则一律用that来连接。

E.g. It is my mother who／that cooks every day.

E.g. It was yesterday that Tom passed in the maths exam．

二、使用本句型的几个注意事项 1．被强调成分是主语，who／that之后的谓语动词应该在人称和数上与原句中的主语保持一致。

e.g. It is I who am right．

e.g. It is he who is wrong．

e.g. It is the students who are lovely．

2．即使被强调成分是句子中的时间状语，地点状语，原因状语等，也不能用when，where, because，要用 that。

E.g. It was after the war was over that Einstein was able to come back to his research work again .

E.g. It was in front of the bank that the old lady was robbed．

E.g. It was because of the heavy rain that he came late．

3．如果被强调的成分有同位语，同位语也应提前。

It was from him，his chemistry teacher，that Paul learned to watch carefully in class．

4．被强调成分是作主语的代词，用主格，是作宾语的代词，用宾格

It was he that helped me yesterday. It was me that he helped yesterday.

5．被强调部分既包括人又包括物，用that不用who

lt was the things and people that they remembered that they were talking about．

三、区分定语从句和强调句型 某些定语从句和强调句型形式差不多，容易混淆。如果去掉it is／ was ...that句子仍然通顺成立，则为强调句型，不成立不通顺，则为定语从句。

E.g. It was three years ago that he went to American for a further study·去掉It was that句子为Three years ago he went to America for a further study．句子通顺，意思完整，那么，这就是一个强调句型。