His eyes were so tired that he had difficulty focusing it.

他的眼睛累了，无法准确聚焦。

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His eyes were so tired that he had difficulty focusing them.

他的眼睛累了，调节焦距困难。

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A child will have difficulty focusing his or her attention, if the proprioceptive system is not fully formed or integrated yet.

如果本体感受系统没有完全形成或者仍未一体化，则孩子难以专注。

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The new AF Focus Illuminator is a supplemental light included for those times when auto focus has difficulty focusing in dark places, or in scenes with particularly low contrast.

ENGADGET: Olympus Stylus TG-625 Tough adds AF light for tricky shots in rough situations

It is typical during initial post-trauma weeks to have difficulty sleeping, eating or focusing on other things.

WSJ: First Responders Seek Out Counseling as Attitudes Shift

Given the difficulty of changing such attitudes, it's not surprising that the government is focusing on making examples of foreigners like Keeler.

CNN: ASIANOW - TIME Asia | Pedophile Playground