Most viruses that cause swine flu or bird flu are very hard to pass from one human to another; they don't cause, epidemics. Sometimes, however, further changes in gene create a virus that can spread rapidly among humans, and can produce a more severe illness. One reason this illness is more severe is that the virus is so new. The regular flu that comes each year is caused by a regular human influenza virus that often has similarities to the viruses that have caused the flu in years past, so people have some degree of immunity to the latest virus. The unusual swine flu or bird flu viruses that develop the ability for person-to-person spread are so different that people have little or no immunity to them.

　　The worst global pandemic in modern times was the influenza pandemic of 1918 to 1919. It affected about a third of the human race, and killed at least 40 million people in less than a year---more than have been killed by AIDS in three decades. The world economy went into a deep recession. The average length of life dropped for 10 years.

　　Unfortunately, the new swine flu virus can be transmitted between humans. It is not clear yet how easily it is transmitted, nor how it is transmitted. Almost surely it is transmitted by sneezing and coughing, and by skin-to-skin contact with an infected person.

　　注意：此部分試題請在答題卡2上作答。

　　52. According to the passage, a pandemic .

　　A) proves to be identical to an epidemic.

　　B) always follows an epidemic.

　　C) tends to be widespread and produces more serious disease

　　D) turns out be fatal to people who get infected

　　53. What can we know about the present epidemic ---swine flu?

　　A) The genes of the flu virus come from pigs.

　　B) It will soon spread and cause a pandemic.

　　C) There has been further change in the genes of the viruses.

　　D) It is similar to the influenza pandemic of 1918 to 1919.

　　54. Why is the swine flu very dangerous to humans?

　　A) Because it is fatal and has killed many people.

　　B) Because it has spread to many countries.

　　C) Because people know nothing about it.

　　D) Because people know no immunity to it.

　　55. What can know about the influenza pandemic of 1918 to 1919?

　　A) It is the only large-scale epidemic in modern times.

　　B) It killed about one third of the world’s population.

　　C) It killed more people than AIDS did.

　　D) It had a great impact on the world’s economy.

　　56. What do scientists say about the transmission of the swine flu virus?

　　A) It is easily transmitted from person to person.

　　B) It remains unclear how it is transmitted.

　　C) It is transmitted by sneezing or coughing.

　　D) It is transmitted by skin-to-skin contact.