There are many varieties and grades of paper materials, and whilst it is fairly easy to spot the varieties, it is far more difficult to spot the grades.

纸张材料有许多品种和等级，虽然很容易分辨它们的种类，但要分辨它们的等级就困难得多了。

youdao

The geography paper was difficult.

地理试卷很难。

youdao

Paper had already existed in China, but the process for producing it was difficult and the paper was of low quality.

中国已经有纸了，但是生产纸的过程很困难，而且纸的质量也很差。

youdao

Can you tell us about the most difficult assignment or paper that you've had to do?

你能给我们讲一讲你最难的一次任务或者论文吗？

考试考砸了怎么办 - SpeakingMax英语口语达人

He said he would not "paper over the difficult decisions" but maintained the party had had several victories in government, including more apprenticeships and more free childcare.

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The committee promises a paper later this year that will address the difficult questions it has dodged for now.

ECONOMIST: Well-cushioned in Basle?

He says not only are the logistics of installing paper ballots difficult, he doesn't know why advocates think it's an improvement.

NPR: Local Election Officials Oppose Paper Ballots