wątpliwy Englisch:

It is doubtful whether this will work.

I am doubtful of his success.

Whether or not he will come is doubtful.

It is doubtful if we can get the engine working.

It's doubtful if we'll finish in time for Christmas.

It's the answer that led those who've been told for so long, by so many, to be cynical and fearful and doubtful about what we can achieve, to put their hands on the arc of history and bend it once more toward the hope of a better day.

He was doubtful about which way to take.

The correctness of the information is doubtful.

Mrs. Harris is very doubtful about her son's future.

I think it doubtful whether he understood my explanation.

We are doubtful about the train leaving on time.

I'm doubtful about what I ought to do.

One thing remains doubtful.

He was doubtful at first but soon came to embrace my advice.

He also came up with yet another doubtful conclusion.

I think his job resume is questionable.

I've done questionable things.

It's questionable whether these vitamins are benefitial at all.

The timing of this is also highly questionable.,

She is a tender girl of questionable morals.

He also brought out one more dubious conclusion.

I'm dubious about claims to speak more than five languages fluently.