pen是可数名词。pens是pen的第三人称单数和复数。
pens：n.笔；钢笔；圈；围栏；畜栏；v.写；(把…)关起来，圈起来；
例：
Whos pinched my pen?
谁拿了我的笔？
相关介绍
Farmers were encouraged to keep their livestock in pens rather than letting them roam freely。
鼓励农民们把家畜关进栏圈，而不是让它们到处乱跑。
These fountain pens last a long time。
这种钢笔且使呢。
These two pens are alike except that they're different colours。
这两支笔样儿差不多，色儿不一样。
There is an overflow of cheap ballpoint pens in the market。
市场上圆珠笔泛滥。
Will students use pens and paper in the future？
将来学生会使用笔和纸吗？
