Drug companies are allowed to be monopolists in the drugs they discover in order to A. increase the overall welfare of society through better health because drug companies continually produce better medications. B. increase the availability of expensive but useful medications. C. encourage research.

C. Encourage research

Explanation:

If a drug company discovers a new drug , it can apply for availing a patent for the same which shall grant it exclusive right to produce and sell the drug in the market for several years.

In such cases, the government tests such drugs if those are genuine before approving such a patent which creates the situation of a monopoly whereby the pharmaceutical company becomes the single seller of such drugs.

The purpose behind creation of such sort of monopolies being, this serves as an incentive or the encouragement for such pharmaceutical companies to carry out extensive research and thereby discover new drugs whose discovery would ultimately lead to common welfare.  

answer; enforce the rules;

answer; the correct answer is (direct foreign investment);