Q:

Execute bash script from one into another directory?

I have 3 directories: 
/A/B/C and 1 bash script in C directory. 
How can I execute this bash script from A into in C directory.

A:

I understand from your comments that you want your script to have its current working directory to be in A/B/C when it executes. Ok, so you go into directory A:
cd A

and then execute script.sh from there:
(cd B/C; ./script.sh)

What this does is start a subshell in which you first change to the directory you want your script to execute in and then executes the script. Putting it as a subshell prevents it from messing up the current directory of your interactive session.
If it is a long running script that you want to keep in the background you can also just add & at the end like any other command.

