Listening comprehension is the key to the command of any foreign language. That '; s one of the reasons why it '; s so difficult to learn on your own.

听力是掌握任何一门外语的关键，这也是它为什么自学起来如此困难之原因所在。

youdao

It 's so difficult a question that none of us can answer it.

那是一个很难的问题，我们没有一个人能回答。

youdao

"I was one of these teenagers, and so I know how difficult it can be to break this habit when it's been with you for a long time,".

VOA: standard.2009.06.22

It's the vocabulary, it's the complexity of the thought, and so on that makes it difficult. Iser acknowledges this.

是词汇，思想的复杂性等等,使它变得难懂，伊瑟尔承认这一点。

耶鲁公开课 - 文学理论导论课程节选

it's very difficult when one is so articulate and is able to express exactly what you want to say,

当一个人已经熟谙一门语言，能够用这门语言清楚明白地表达意思，

想学好英语吗？ - SpeakingMax英语口语达人

The U.S. has traditionally refrained from imposing duties on supposedly subsidized imports from nonmarket economies because it's so difficult to break out what the actual subsidies are for each company and industry.

FORBES: Magazine Article

"It's so difficult to quantify, " said Alejandro Moreno, a former MLS Cup winner with Columbus and now a soccer analyst.

WSJ: Is Thierry Henry Worth the Money?

"It's so difficult to take other factors into account - for example, moderate drinkers might have a better social environment, " he told BBC News Online.

BBC: Alcohol 'improves IQ'