—can you go swimming with us this afternoon?

—Sorry, I can't.  I______ do the chores at home.[ ]

A.  can    

B.  could    

C.  can't    

D.  have to

口呼吸引起的错畸形表现不包括（）.

A.上前牙前突

B.上牙列拥挤

C.上牙弓狭窄、腭盖高拱

D.上牙弓宽大、出现间隙

E.下颌后缩