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 43 to 50.

          Smallpox was the first widespread disease to be eliminated by human intervention. Known as a highly contagious viral disease, it broke out in Europe, causing the deaths of millions of people until the vaccination was invented by Edward Jenner around 1800. In many nations, it was a terror, a fatal disease until very recently. Its victims suffer high fever, vomiting and painful, itchy, pustules that left scars. In villages and cities all over the world, people were worried about suffering smallpox.

          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 the public to aid health workers. One by one, each small-pox victim was sought out, 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

The word “threat” in paragraph 2 could best be replaced by________