In the flash cards is this: 你不这道这个是什么吗？
Why is 吗 used when 什么 is used? I thought the 吗 could be dropped in this instance?
it's turning it into a yes/no question.
so instead of meaning "you don't know what this is."
it now means "you don't know what this is, do you?"
Thank you, that makes sense.
Exactly what Ciaran said. 😊
btw there's also an error in that sentence.
You probably meant "你不知道这个是什么吗？"