It is said that personal space ranging from 2 to 4 feet is t

It is said that personal space ranging from 2 to 4 feet is the distance___to separate……空格填什么
It is said that personal space ranging from 2 to 4 feet is the distance___to separate people waiting in lines,so you have to wait behind the yellow line in the bank.
A.maintaining
B.maintains
C.maintained
D.having maintained
要原因和翻译,