But making the vaccine more widely available especially in rural areas has been difficult.

VOA: special.2009.11.03

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

I want to illustrate one of the reasons why it has been so difficult to get a grasp on the hair cells in the inner ear.

我想用图例为大家说明一下,为什么难以捕获内耳中的毛细胞。

斯坦福公开课 - 7个颠覆你思想的演讲课程节选

But the timing of its opening in January has been difficult.

VOA: special.2010.03.31

The president acknowledged the release of the memos has been difficult for the intelligence community.

VOA: standard.2009.04.20

"He came in with high hopes of a lot of Americans and with a lot of support, and legislating some of those goals has been difficult,"

VOA: standard.2009.12.29

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

She adds that depression has been linked to babies who are more difficult to console.

VOA: standard.2010.03.03

"I think that would be difficult to achieve at Fort Hood, given the national media attention that has been focused on the Fort Hood community,".

VOA: standard.2009.11.10

Much of the company has been privatized in recent years, but many workers are civil servants and it is very difficult to lay them off in France.

VOA: standard.2010.04.11

just to make it more difficult for them to operate. Shaaf also says that the government has been using whatever laws it can to shut down organizations dedicated to civic activism.

VOA: standard.2009.08.04