1
verb + doubtfully
She smiled doubtfully.
她怀疑地笑了笑。
怀疑地；迟疑地；含糊地
先理解核心含义，再看它在真实句子里的用法。
怀疑地；迟疑地；含糊地
in a way that shows doubt or uncertainty
She smiled doubtfully.
她怀疑地笑了笑。
怀疑地；可疑地。
In a doubtful manner, in context of doubt or ambiguity, questionably.
She picked up the old coin and examined it doubtfully.
她拿起那枚旧硬币，怀疑地仔细端详。
He doubtfully asked whether the train would arrive on time.
他怀疑地问火车是否会准时到达。
They looked at each other doubtfully before entering the dark room.
他们怀疑地互相对视，然后才走进那间黑暗的房间。
She smiled doubtfully.
她怀疑地笑了笑。
doubtfully 作方式状语，常修饰表示看、说、想等动作的动词，说明动作带有怀疑态度。
He studied the contract doubtfully.
他怀疑地研究那份合同。
Not this
She looked at me doubtful.
Use this
She looked at me doubtfully.
修饰动词looked应用副词doubtfully，而不是形容词doubtful。形容词不能修饰动词，需加-ly变成副词。
Not this
He will doubtfully pass the exam.
Use this
He will doubtlessly pass the exam.
doubtfully意为“怀疑地、不确定地”，而doubtlessly意为“无疑地、肯定地”。二者意思相反，想表达“肯定会”时应用doubtlessly。
Focus on the distinctions below. Other candidates are kept compact until a reliable usage note is available.
怀疑地看着
She looked doubtfully at the strange dish.
她怀疑地看着那道奇怪的菜。
怀疑地摇头
He shook his head doubtfully when asked if the plan would work.
当被问及这个计划是否会奏效时，他怀疑地摇了摇头。
怀疑地问
"Are you sure?" she asked doubtfully.
“你确定吗？”她怀疑地问。
怀疑地瞥了一眼
He glanced doubtfully at the price tag.
他怀疑地瞥了一眼价签。
怀疑地审视
The doctor regarded the patient's symptoms doubtfully.
医生怀疑地审视着病人的症状。
怀疑地听着
They listened doubtfully to his explanation.
他们怀疑地听着他的解释。
Use doubtfully naturally, then get feedback on meaning, tone, grammar, and phrasing.
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doubt（怀疑）+ fully（满满地）：心里装满问号，行动就迟疑含糊，即doubtfully（怀疑地）。
语域：formal 常见场景：书面叙事、正式写作 doubtfully 多用于书面叙述或较正式的语境，表示以怀疑、不确定的态度做某事；口语中更常改用 not sure 等表达。
在 doubtfully /ˈdaʊtfəli/ 中，重音在第一音节，'doubt' 发 /daʊt/。'doubt' 和 'doubtful' 与它的第一部分读音相同。所有以 '-fully' 结尾的副词（如 carefully、thoughtfully、faithfully）后缀都读 /fəli/，但重音元音不同，并不与 doubtfully 押韵。注意 thoughtfully 拼写与 doubtfully 相似（都有不发音字母且以 -fully 结尾），但元音是 /ɔː/ 而不是 /aʊ/。
Dictionary facts from ECDICT, WIKTIONARY.