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Directions: Reading Comprehension - read the following passage to answer the question below.

1Polio, a viral disease that, amongst other things, causes headache and vomiting, in addition to abnormal reflexes and back stiffness, wrecked havoc on the world's human population.2 In 1955, however, a man named Jonas Salk, of the University of Pittsburgh, created the world's first working polio vaccine.3 Salk's vaccine utilized a "killed virus", wherein the vaccine contains destroyed virus particles that cannot replicate, but has enough intact proteins to evoke a response from the body's immune system.

4That polio was considered the worst disease following the World Wars, the vaccine for it was considered a great boon to human society.5 Two years after the vaccine was first developed, 100 million doses had been distributed across the United States.6 The vaccine's efficacy could be understood through the world's expert scientists; figures in Denmark reported only a few failures of the vaccine to stop polio out of 2,500,000 cases.

7For his success, Salk became an international hero and a household name. Considering the staggering success of Salk's polio vaccine, Salk pursued another great challenge: eliminating AIDS and HIV.8 Although Salk's efforts against AIDS and HIV didn't prove as fruitful as his polio vaccine, the entire body of his work was important and significant, as it improved the lives of a countless number of individuals, perhaps in the range of millions.

Select the sentence that indicates how the Salk vaccine operated. Enter your choice in the blank below. (Ex: 3)


Response:





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