若全集$U=\left\{1,2,3,4,5,6\right\},M=\left\{2,3\right\},N=\left\{1,4\right\}$,则集合$\left\{5,6\right\}$等于（  ）

用适当的词补全对话。

A: Do you know we have a new teacher and two new students this semester?

B: Really? What ____ the new teacher look ____?

A: He is an old man. He ____ no hair.

B: Is he ____?

A: Yes. And he ____ glasses.

B: ____ he have a mustache?

A: No, he ____ a beard. He is not good-looking. But he is very kind.

B: What ____ your new classmates? What ____ they ____ like?

A: They are twins. They look the ____. They ____ of medium height. They're not heavy ____ thin. They ____ curly hair.

B: What's the ____ ____ their hair?

A: Well, they ____ blonde hair. They are good-looking.