Copulas
n. 系动词（如be,seem,appear等）, （命题主词与谓词间的）连系( copula的复数形式 )
🗣️ 情景例句
Take it side again .... OK, and switch. Stretch it out.
再侧身……好 左右交替。尽量伸展。
You'll get hurt, if you don't watch out.
你不注意的话，就会受伤。
My shoe has been pressing against my foot, so it hurts a bit.
我的鞋一直挤着脚，所以脚有点疼。