单项选择。

— What's John doing now?

— He ______ a letter. [ ]

A.is writing

B.are writing

C.is writening

D.be writing

下列句子中通假字判断及其解释错误的一项是【  】

A．自掊击于世者也被动句，介宾短语后置句

B．又奚以自多壮语后置

C．有购木、钻燧于夏后氏之世者状语后置

D．宋人有耕者定语后置