预防接种的目的是（）
A.提高人群易感性
B.降低人群易感性
C.提高人群非特异免疫水平
D.降低人群非特异免疫水平
E.以上都不是
参考答案：B
The newly built café, the walls of _____ are painted light green, is really a peaceful place for us, especially
after hard work. [ ]
A. that
B. it
C. what
D. which
脊柱结核易发生于
A．颈椎
B．胸椎
C．腰椎
D．骶尾骨
E．胸腰椎
