1. He is an author of doubtful reputation.
   他是一位名声不太好的作家。
2. I was doubtful of my judgement.
   我对自己的判断拿不准。
3. It is doubtful whether it is true or not.
   这件事的真假是可疑的。
4. I feel very doubtful about this.
   我对这点很怀疑。
5. I am very doubtful of that.
   我很疑心那件事。
6. The day is doubtful.
   胜负难料。
7. This is a doubtful battle.
   这是一场胜负难测的战争。
8. He is a doubtful character.
   他是一个不可靠的人。
9. I'm doubtful where to go.
   该往哪里去我心中无底。
10. 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。
11. 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、小面馆使用这种可疑猪油很普遍。
12. Taxus L. is a problematic genus, not only its species are discouragingly similar, but also its family circumscription are still doubtful.
    红豆杉种属的问题，不但它的种类惊人地相似，而且其科的界限也非常模糊。

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