Faculative
a. 允许的, 任意的, 兼性的, 偶发的
🗣️ 情景例句
When does he arrive?
他什么时候到？
I'll walk you to the door.
我送你到门口。
Imagine a pen attached to the weight in such a way that its point rests upon a piece of paper on the floor.
假定把一支笔拴在重物上，笔尖落在地板上的一张纸上，