He is an author of doubtful reputation.

他是一位名声不太好作家。

I was doubtful of my judgement.

我对自己判断拿不准。

It is doubtful whether it is true or not.

这件事真假是。

I feel very doubtful about this.

我对这点很。

I am very doubtful of that.

我很心那件事。

Examination result is appalling, urban chophouse, small noodle shop uses this to plant doubtful and lardy very general.

检查结果令人震惊,市区小餐馆、小面馆使用这种猪油很普遍。

I am doubtful whether I could ever learn English, but I'm determined to have a bash at it.

不晓得我能不能学会英语, 但是我决心试试看。

The day is doubtful.

胜负难料。

This is a doubtful battle.

这是一场胜负难测战争。

He is a doubtful character.

他是一个不靠人。

I'm doubtful where to go.

该往哪里去我心中无底。

Taxus L. is a problematic genus, not only its species are discouragingly similar, but also its family circumscription are still doubtful.

红豆杉种属问题，不但它种类惊人地相似，而且其科界限也非常模糊。