Three mod a, b, c in a crate, how to use mod a in mod b?

help
1

I have three mod a, b, c in a crate, but I can't find a way to use a in mod b, what is the statement?

src
   a
     mod.rs
   b 
     mod.rs
   c
     mod.rs
2 
// a/mod.rs
use super::b;
3

Thanks a lot.

4

https://doc.rust-lang.org/stable/reference.html#use-declarations