Can't do it, tried, can't...So Help!

A row of lockers numbered 1 through 100.
-Person A walks by and closes all the doors that are multiples of 2.
-Person B closes all doors that are multiples of 3 and opens the ones that are closed.
-Person C closes all doors that multiply by 4 and opens the ones that are closed.
-Etc, etc, etc until person number 100 walks by and changes only locker 100.

Which lockers are open at the end of this process??

Shari
Mom to DS 10, DS 11, DS 13
Ability doesn't make us, Choices do!