curtain 可数不可数？

curtain是《join in 》小学剑桥英语四年级第8单元的单词：curtain是可数名词：课文中有两个例子：
1. There is a rabbit behind the curtain.（窗帘上开的，兔子藏在一边）
2.You look behind the curtains.
3. It was ten in the morning but the curtains were still drawn( closed)已是早上十点了，可窗帘还拉着。
只有作为（舞台上的）幕，帷幕就没在复数形式：
It's time to face the final curtain.人生的戏该落幕了。
The audience is waiting for the curtain to rise.观众们正等待开幕。

不可数