SF-36评价量表研究形成的单位是
A、东京大学医学院
B、美国波士顿健康研究所
C、美国国家疾病预防控制中心
D、世界卫生组织
E、美国食品与药品管理局
参考答案:B
Nobody knows for sure how dinosaurs died out 65,000,000 years ago. It _______ because of sudden changes of their living conditions.
A.must have happened
B.would have happened
C.should have happened
D.might have happened
化验室以哪种灭火器为主要灭火工具,为什么?