doubtful about的用法和樣例：
例句
- I am doubtful about the value of your proposal.
我懷疑你的提議是否有價值。 - I am doubtful about the propriety of granting such a request.
我懷疑答應這項要求是否合適。 - I'm rather doubtful about his integrity.
我對這事的忠誠頗有懷疑。 - Because of a long drought, the farmers are doubtful about the prospect of a good yield.
因為長時間的乾旱，農民們對於好收成的前景是懷疑的。
