How was the public motivated to help health workers?

Câu hỏi: Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 30 to 34.
Smallpox was the first widespread disease to be eliminated by human intervention. In May, 1966, the World Health Organization (WHO), an agency of the United Nations was authorized to initiate a global campaign to eradicate smallpox. The goal was to eliminate the disease in one decade. At the time, the disease posed a serious threat to people in more than thirty nations. Because similar projects for malaria and yellow fever had failed, few believed that smallpox could actually be eradicated but eleven years after the initial organization of the campaign, no cases were reported in the field.
The strategy was not only to provide mass vaccinations but also to isolate patients with active smallpox in order to contain the spread of the disease and to break the chain of human transmission. Rewards for reporting smallpox assisted in motivating so that patients are removed from contact with others and treated. At the same time, the entire village where the victim had lived was vaccinated.
By April of 1978 WHO officials announced that they had isolated the last known case of the disease but health workers continued to search for new cases for additional years to be completely sure. In May, 1980, a formal statement was made to the global community. Today smallpox is no longer a threat to humanity. Routine vaccinations have been stopped worldwide.
How was the public motivated to help health workers?
A. By educating them
B. By rewarding them for reporting cases
C. By isolating them from others
D. By giving them vaccination