He says those questions became even more difficult to answer after the 9/11 attacks by a group of Sunni Arab terrorists that killed 3,000 people on American soil, and after the massive U.S.military deployments in Afghanistan and Iraq.

VOA: standard.2010.03.18

He says, oh it's a very simple question; it's not difficult to answer.

他答道,这问题太简单了,一点儿都不难回答

耶鲁公开课 - 古希腊历史简介课程节选

Now, that's actually a difficult question to ask-- to answer for a child, but I tried my best to give him an answer.

向一个孩子解释这个问题其实挺困难的，但我还是尽力给了他一个答案。

耶鲁公开课 - 心理学导论课程节选

The question of who could win such an unusual contest is difficult to answer.

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So, I think this question will be fun to answer, but it may be difficult to answer.

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Though there are signs of change, it is difficult to answer those questions with an overwhelming yes.

CNN: MONEY & INVESTING