doubtful
adj. 怀疑的，不确定的；未必的，不大可能的；不可靠的
例句
We were doubtful about the practicability of the plan.
我们怀疑这个计划是否切实可行。
《牛津词典》
This wine is of doubtful quality.
这酒的质量有问题。
Rose was doubtful about the whole idea.
罗斯对整个设想持怀疑态度。
