26 all bird species are thought to be susceptible to infection, domestic poultry flocks are especially vulnerable to infections that can rapidly reach epidemic proportions.
答案：(B) While
While 在此是「雖然、儘管」的讓步用法：雖然所有鳥類都可能受感染，家禽群卻特別容易爆發大規模疫情；Not、Since（因為）、Unless（除非）都不合。
答對率 26%。
while 你先學到的一定是「當…的時候」（While I was cooking, the phone rang.），所以看到句首的 While 就往時間去想，讀不出轉折。它還有一個同樣常考的意思：「雖然、儘管」，功能等同 although。
看前後兩個子句是「同時發生」還是「互相對比」。本句前半說「所有鳥類都可能受感染」，後半說「家禽群特別容易爆發疫情」——一個是普遍情況、一個是特例，屬於對比，所以是讓步用法。再看句中的 especially（特別是），也在標示這是從普遍中拉出特例。
while 還可以表示「而、然而」，用來並列兩個相反的事實：Some people like coffee, while others prefer tea.（有些人愛咖啡，有些人則偏好茶）。
While…, …（雖然）、although（雖然）、whereas（而、然而）、be susceptible to（易受…影響）。
Avian influenza, or "bird flu," is a contagious disease caused by viruses that normally infect only birds and, less commonly, pigs. 26 all bird species are thought to be susceptible to infection, domestic poultry flocks are especially vulnerable to infections that can rapidly reach epidemic proportions.
Outbreaks of avian influenza 27 be devastating for the poultry industry and for farmers. For example, an outbreak of avian influenza in the USA in 1983–1984 resulted in the destruction of more than 17 million birds 28 nearly US$ 65 million. Economic consequences are often most serious in developing countries 29 poultry raising is an important source of income, and of food, for impoverished rural farmers and their families.
When outbreaks become widespread within a country, control can be extremely difficult. 30, government authorities usually undertake aggressive emergency control measures as soon as an outbreak is detected.