When the patent is running out of a drug that made the company a lot of money
a. they find various ways to extend its patent, including making minor changes in its contents
b. they will try to get its users to switch to its new, patent-protected and therefore expensive new version
c. they will give it away for free as "samples" to try to get doctors hooked on prescribing it and patients used to taking it
d. all of the above
