The success of the system is not in doubt.

这种制度的成功确定无疑。

The outcome was still in doubt.

结果仍不确定。

His inclusion in the team is in doubt.

他是否能被选入这个队还未定案。

His intellect and mental agility have never been in doubt.

他的才智和头脑的敏锐从未被受到怀疑。

All the time you are in doubt about the cause of your illness, you are fighting against an invisible enemy.

一直以来你都在怀疑自己的病因，你是在和一个无形的敌人斗争。