General Allyn says U.N.and Haitian forces continue to have lead responsibility for security, which he says has been mostly good in very difficult circumstances.

VOA: standard.2010.01.19

Why has it been so hard and why does it continue to be difficult to identify these pluripotent cells within tissues?

为什么会那么难呢,为什么在组织中识别多能干细胞,始终困难重重呢

耶鲁公开课 - 生物医学工程探索课程节选

But for all that, thinking about those facts make it rather difficult, while you're thinking about the facts, to continue enjoying kissing the person.

但是尽管如此，想到这些事实让继续享受亲吻，变得困难了，当你想到这些事实时。

耶鲁公开课 - 死亡课程节选

"If the current posture of the Israeli government on Gaza continues it would not be difficult to predict that Turkish and Israeli relations will continue to be difficult and fragile,"

VOA: standard.2009.10.27