条件从句

主句

If

主语+were to/ should +动词原形+其它

主语 + would + 动词原形  + 其它

If

I were to do the experiment,

I would do it some other way.

If

it should rain tomorrow,

we would stay at home.

If

I were to be young again,

I should make good use of my time.

If

you were to try again,

you might succeed.

If

he should be sick,

he would send for a doctor.