三張紙單數還是複數

仍然是單數，因為紙paper 為不可數名詞，可量詞張piece 需要用複數。

例如

I grabbed three pieces of paper to takenotes on.

我抓過三張紙來記筆記。

The researchers then compared the artificially aged samples to the real deal: three pieces of paper crafted in 15th-century Europe.

然後研究者比較了人工老化的樣本和真實的紙張