[译] 我怀疑他是否能及时交房租。
[误] I doubt that he can pay for the rent in time.

[正] I doubt whether he can pay for the rent in time.
[注] doubt 用在肯定句中，通常要用 whether 或 if 来引导其宾语从句，只有在否定句或疑问句中，doubt 的宾语从句才能用 that 引导。如：Do you doubt that the mayor will be able to attend the meeting? 你怀疑市长会来出席这次会议吗？