对。。be comfortable doing sth
表语形容词通常用不定式作补足语。但comfortable作表语如果用不定式作补足语，则不定式必须为悬空不定式，即句子主语为不定式的逻辑宾语。例如：The clothes are comforable to wear. 所以如果comfortable作表语需要补足，而句子主语与非谓语动词为主动关系时，就不能用不定式作形容词补足
语，而用in doing sth或doing sth.如果不用介词，则
doing sth分析为现在分词作comfortable的补足语。句型为：
Sb is comfortable (in) doing sth.
= sb feels confident in doing sth.
be comfortable doing sth.在做某事方面是舒适的，舒适地做某事（doing sth.作状语）= be comfortable about/with sth.
(about/with sth.作状语）
I am comfortable learning English.= I am comfortabe about/with Englishlearning.
有类似用法的词语还有：
have trouble doing sth./with sth.be busy doing sth./with sth
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