pen是可数名词。
pen
n.笔;钢笔;圈;围栏;畜栏
v.写;(把…)关起来，圈起来
第三人称单数 pens
复数 pens
现在分词 penning
过去式 penned
过去分词 penned
Please write in pen on both sides of the paper.
请用自来水笔在纸的.正反两面书写。
Go and get me a pen please.
请你去给我拿支钢笔来。
I could hear his pen scraping across the paper.
我听得见他的钢笔在纸上沙沙地响。
