mary is play the piano划线提问,一般疑问句,否定回答.划线：the piano

mary is play the piano划线提问,一般疑问句,否定回答.划线：the piano
mary is play the piano划线提问,一般疑问句,否定回答.划线：the piano

mary is play the piano划线提问,一般疑问句,否定回答.划线：the piano
Is Mary playing the piano?
No,she isn't.

what is mary playing？
the piano.
这叫特殊疑问句。