"the dubiousness of his claim"
"there is no question about the validity of the enterprise"
"I doubt that she will accept his proposal of marriage"
"I doubt these reports"
"I suspect her true motives"
"she distrusts her stepmother"
I doubt of her ability.
我怀疑她的能力。
Such actions make me doubt of his sanity.
这种行为使我怀疑他的神志是否清醒。
How do you doubt of the firm's future?
你怎能怀疑公司的前景呢?