一般来说，如果doubt用于肯定句，引导的宾语从句由if， whether， what， how等词引导，不能由that引导。
I doubt whether the new one will be any better.
如果doubt 用于否定句，引导的宾语从句只能由that引导，或省略that。
I never doubted (that) she would come.
doubt宾语从句的用法
1、The research showed beyond doubt that smoking contributes to heart disease.这项研究确实表明吸烟会导致心脏疾病。
2、She knew beyond a shadow of a doubt that he was lying.她十分清楚地知道，他在说谎。
3、She knew without a shadow of a doubt that he was lying to her.她十分清楚他在对她撒谎。
doubt宾语从句的用法
但是需要符合语法，像“I doubt how to achieve it”这样根本就是语句不通畅，需要将“how”改成“if”，这样的意思就是“我对能否完成这个表示怀疑”
doubt有以下含义
n.
疑惑疑问不确定不相信
v.
无把握不能肯定认为…未必可能怀疑不相信不信任
扩展资料：
例句：
1、N-VAR 怀疑疑虑
If you have doubt or doubts about something， you feel uncertain about it and do not know
whether it is true or possible. If you say you have no doubt about it， you mean that you are
certain it is true.
This raises doubts about the point of advertising...
这对做广告的意义提出了疑问。
2、VERB 不能肯定认为…未必可能
If you doubt whether something is true or possible， you believe that it is probably not true