可以直接用动词原形作系动词be的表语吗

曾老师提到如果谓语为will/would be时，作表语的不定式不可省略to. 我以前没有看到过这种说法。曾老师可否告知这个说法出自哪里。

我查了COCA语料库，would be后用不带to的不定式的为12/200=6%.

is和was后用to do的都是大约8%。

也就是说，主语部分含有实意动词do, 不定式作表语，如果系词be为is 或was, 则绝大多数情况下不定式不带to, 但大约有8%的几率，不定式是带to的。

当系词为will be时，不定式作表语较少，如果用不定式作表语，则通常都是带to的。

当系词为would be时，不定式作表语通常都带to, 但有6%的几率，不定式不带to。也就是说不是绝对不能用不带to的不定式作表语。

以下为COCA例句：

...all I'd want to do would be sleep.

...one of the best things that Obama could do would be build 12-month farmers markets, especially in inner cities.

 All she would have to do would be not get caught until that happened. 

 ...the very first thing you would do would be interview the parents.

 I thought the very least that they would do would be whip me because they whipped people on a regular basis.

 We thought that the best thing to do would be bring in the bloodhounds.

The most graceful thing to do would be just not be there, and that worked out all right. 

Last thing she'd want me to do would be share her nail polish.

 As governor, what I would do would be work very closely with the president and with the Congress to ensure that...

 The best thing to do would be check her in about a year and see how she did. 

All we'd have to do would be bait a trap with fruits or nuts.

...the first thing I would do would be pay off my debts...