The correct choice is (a) Magic bullets
For explanation I would say: In the early 1900s, German Nobel Laureate Paul Ehrlich imagined an ideal therapy for disease, a drug precisely targeted to an invader, which if linked to a toxic chemical would act like a missile, carrying a destructive payload directly to the disease. Ehrlich said the drug would be a ‘Magische Kugel’, which in English means ‘Magic Bullet’. Such a therapy, he theorized, would be ideal for countless diseases, including cancer.