做某事有困難有兩種說(shuō)法：
1. have difficulty doing sth. 其中的分詞短語(yǔ) doing sth. 用作時(shí)間狀語(yǔ),即“做某事的時(shí)候有困難”.
2.have difficulty in doing sth. 其中的介詞短語(yǔ) in doing sth. 用作方面狀語(yǔ),即“在做某事方面有困難”.
3. 還有一種說(shuō)法是 have difficulty doing sth 是 have difficulty in doing sth. 省略了介詞 in.相同的短語(yǔ)還有 have trouble (in) doing sth.（做某事有麻煩）.
因此,I had difficult finding the keyhole 是正確的.當(dāng)然也可以說(shuō)成 I had difficult in finding the keyhole.不過(guò),前者更符合口語(yǔ),后者有些學(xué)究味兒.

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