它的音高越接近第一个音高，对海豚来说就越难辨别出它是低音。

The closer it came in pitch to the first one, the hard it became for the dolphin to correctly identify it as low.

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这两个品种很难辨别。

It's difficult to differentiate between the two varieties.

《牛津词典》

虽然很难辨别哪些包裹里装的是社会保障支票等重要物品，但美国邮政（USPS）和联合包裹服务公司（UPS）会尽其所能优先处理敏感材料。

It can be hard to identify which parcels are carrying crucial items such as Social Security checks, but USPS and UPS try their best to prioritize sensitive material.

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