Q. Widespread resistance of malarial parasite to drugs like chloroquine has prompted attempts to develop a malarial vaccine to combat malaria. Why is it difficult to develop an effective malaria vaccine?

• (A) Man does not develop immunity to malaria during natural infection
• (B) Malaria is caused by several species of Plasmodium
• (C) Vaccines can be developed only against bacteria
• (D) Man is only an intermediate host and not the definitive host