Q: In this task, you need to provide the correct option for a given problem on probability from the provided options.
Problem: in how many ways can 21 books on english and 19 books on french be placed in a row on a shelf so that two books on french may not be together ? 
Options: a ) 3990 , b ) 1540 , c ) 1995 , d ) 3672 , e ) none of these
A:
b