Consider the following statements: AIDS is transmitted I. by sexual intercourse. II. by blood transfusion. III. by mosquitoes and other blood sucking insects. IV. across the placenta. Of these statements

The correct option is B because of the specific ways HIV, the virus that causes AIDS, can be transmitted between humans. Statement I is correct because unprotected sexual intercourse is the most common mode of transmission through infected bodily fluids. Statement II is correct because receiving infected blood or blood products during a transfusion directly introduces the virus into the bloodstream. Statement IV is correct because a mother can pass the virus to her child during pregnancy through the placenta, as well as during childbirth or breastfeeding. Statement III is incorrect because HIV cannot survive or replicate inside mosquitoes or other insects. When an insect bites, it does not inject the blood of its previous victim into the next person, making it impossible for AIDS to be transmitted this way.