There are several research centers in China a certain disease called Bird Flu is
being studied.
A. which
B. where
C. when
D. what
网友回答
A. which
(答案→)B. where
C. when
D. what
解析：考查短语从句。本题定语从句的先行词是several research centers,后面的定语从句句子结构很完整，故使用关系副词where引导这个定语从句。A项是关系代词，C项的先行词要是时间的名词；D项不是定语从句的关系词。句意：在中国有几个研究中心，在这些研究中心里，一种名叫禽流感的疾病正在被研究。故B正确。