他能否来还不确定。

It is ___doubtful he'll be able to come.

那笔钱能否再被找到值得怀疑。

It was ___doubtful that the money would ever be found again.

在塑造个性方面，先天特质是否比生活经历更重要是值得怀疑的。

It's ___doubtful that innate traits outweigh life experiences in shaping personality.