单选题
Although we already know a great deal about influenza, and
although the World Health Organization is constantly collecting detailed
information from its chain of influenza reference laboratories throughout the
world, it is extremely difficult for epidemiologists (流行病专家), who study
infectious disease, to predict when and where the next flu epidemic will occur,
and how severe it will be. There are three kinds of influenza
virus, known as A, B and C. Influenza C virus is relatively stable and causes
mild infections that do not spread far through the population. The A and B types
are unstable, and are responsible for the epidemics that cause frequent concern.
Following any virus attack, the human body builds up antibodies which confer
immunity to that strain of virus, but a virus with the capacity to change its
character is able to by-pass this protection. Variability is less developed in
the influenza B virus, which affects only human beings. An influenza B virus may
cause a widespread epidemic but will have little effect if introduced into the
same community soon afterwards, since nearly everyone will have built up
antibodies and will be immune. The influenza A virus, which affects animals
also, is extremely unstable and is responsible for some of the worst outbreaks
of the disease, such as the unparalleled pandemic, or world epidemic, of
1918-1919, when about half the world's population were infected and about twenty
million people died, some from pneumonia caused by the virus itself and some
from secondary complications(并发症) caused by bacteria. Accurate
prediction is difficult because of the complication of the factors. A particular
virus may be related to one to which some of the population have partial
involved immunity. The extent to which it will spread will depend on factors
such as its own strength, or virulence, the ease with which it can be
transmitted and the strength of the opposition it encounters. Scientists,
however, have a reliable general picture of the world situation. Influenza A
attacks us in waves every two or three years, while influenza B, which travels
more slowly, launches its main assaults every three to six years. The outbreaks
vary from isolated cases to epidemics involving a tenth or more of the
population. We may confidently prophesy that sooner or later large numbers of
people will be feeling the unpleasant effects of some kind of influenza
virus.
单选题
Which of the following is the most appropriate title for the passage?
A.Symptoms of Influenza
B.Man Versus Virus
C.World Health Organization：Forefront against Influenza Virus