[Idiom] in file

[Unregistered]

still I am confusing.

I know when you stnad in a line, one behind the other, you say that "They stood in single file."

1. My book says that "They stood in file" means that there are two lines. Is it right?

2. How do you say when there are four lines, one behind the other?
They stood in four files... correct??

3. How do you say when there are many lines, one behind the other?
They stood in files????

please help me

 

[Tdol]

1. My book says that "They stood in file" means that there are two lines. Is it right?
No