I am a little doubtful about this plan.

我对这个计划有几分怀疑。

He felt doubtful about the success of the project.

他对项目的成功感到怀疑。

We were doubtful about the product's usefulness from the start.

我们从一开始就怀疑产品的实用性。

I'm rather doubtful about its reliability.

我很怀疑其可靠性。

He was doubtful about accepting extra work.

他拿不定主意是否接受额外工作。

I am doubtful about the chances of success.

我对成功的可能性半信半疑。

Paul Wignall, a geologist at the University of Leeds, had always been doubtful about the meteor theory.

利兹大学的地质学家Paul Wignall一直对天体碰撞论持怀疑态度。

Bush administration has been feeling confused, anxious and doubtful about whether the Iraqi government can deliver on its promise to stabilize the country.

美政府一直以来都因为伊政府说出保证是否能稳固国家而感到怀疑及焦虑。