what color is your pen A it is red B it is a red C it is a red pen

选A it is red
题目是问what color is your pen 你的笔是什么颜色的?
回答应该是 it is red 它是红色的
it is +adj.加上表示颜色的形容词,如 it is black/ white/ green
不能像B那样,在形容词前面加a
如果要加a的话,应该像C那样 it is a red pen
it is a/ an +adj.+n.
不过这时候问句应该是 What's this?这是什么?----It is a red pen.这是一支红笔