doubt既可以作名词也可以作动词
There is some doubt whether he can come today.(doubt名词，用于肯定句时，用whether引导同位语从句)
There is no doubt that he will come today.(否定句用that引导同位语从句)
I never doubted (that) she would come.(doubt动词，前面有否定副词时，用that引导宾语从句)
我从未怀疑过她会来。
I doubt whether/if the new one will be any better.(肯定句用whether/if引导宾语从句)
我不敢肯定这个新的是否会好些。
1. 作为动词,意为"怀疑"
例句:I doubt his honesty. 我怀疑他的诚实。
2. 作为名词,意为"疑问,疑虑"
例句:I have doubts about his plan. 我对他的计划有疑问。
There are still doubts whether he is suitable for this job. 对他是否适合这份工作还有疑虑。
3. no doubt 为副词词组,意为"无疑,必定"
例句:No doubt this is the best choice. 这无疑是最好的选择。
4. in doubt 意为"不确定的"
例句:The matter is still in doubt. 这件事情还不确定。
5. beyond doubt 意为"毫无疑问地"
例句:It has been proved beyond doubt. 这已经毫无疑问地被证明了。
6. without a doubt 意为"毫无疑问,必定"
例句:Without a doubt, he is innocent. 毫无疑问,他是无辜的。
