be doubtful of

基本解釋

If you have sorrowful past, perhaps he would be doubtful of your heart.
如果你的過去不是很快樂，也許他要懷疑你的心了。
And seek not ye what ye shall eat, or what ye shall drink, neither be ye of doubtful mind.
你們不要求喫什麼，喝什麼，也不要掛心。
And if you do take one, you'll probably make the shop assistants feel unease, they might be doubtful of your intentions.
倘若你自己帶著拎包進店，反倒會使店家覺得不踏實，沒準會懷疑你是扒手呢！

"Well they certainly will be doubtful of it unless President Obama makes a strong argument.

But the Scottish secretary's job, which will be of doubtful value once all law-making and spending responsibility has been passed to the Scottish parliament, looks to have been made completely redundant by the new committee.
ECONOMIST: The constitution
One clear danger is that they may alienate customers, who will welcome better service but may be more doubtful about uses of the technology such as finely segmenting the market or targeting customers individually.
ECONOMIST: Always-on people
It's the answer that led those who have been told for so long by so many to be cynical, and fearful, and doubtful of 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.
NPR: Transcript Of Barack Obama's Victory Speech