There is Mr.Smith at the door who wants to speak to you.
A.a some B.certain C.some a D.a certain
There is Mr.Smith at the door who wants to speak to you.
A.a some B.certain C.some a D.a certain
D
a certain Mr Smith或some Mr Smith意为“一个姓史密斯的先生”。因此A、B、C三项的用法都不对。