President Pierce found it difficult to control them.

VOA: special.2009.04.16

There may be circumstances under which it's the case but it's often difficult to control.

可能在某些环境下可以做到,但是通常情况下很难控制。

麻省理工公开课 - 热力学与动力学课程节选

The question is not so much how we control what happens to us but what do we do when we were faced difficult circumstances, and how we can make spiritual meaning even when difficult things happen to us.

问题不是我们能够掌控多少,而是当我们面对困境,能做些什么，我们怎样体现灵性的意义,即便我们面临困境。

普林斯顿公开课 - 人性课程节选

And it was difficult to control.

VOA: special.2009.09.10

However,this is more difficult because it is harder to control the diets of people and because they live longer than other animals.

VOA: special.2009.09.01

Unless carbon emissions are brought under control,he says, the challenge of adapting to global climate change will become ever more difficult.

VOA: standard.2010.06.14