餐厅服务员都用盖子熄灭酒精灯火锅，该灭火的主要原理是[ ]
A.清除可燃物
B.降低可燃物的着火点
C.隔绝空气
D.使可燃物的温度降低到着火点以下
答案：C
Modern China is experiencing a completely new period_____respect for science and creativity has become the guiding principle of society．
A．which
B．where
C．in which
D．that
某患儿，"方颅"、"枕秃"、"串珠胸"，夜间经常啼哭，导致这些症状最可能的原因是
A．铁缺乏
B．维生素A缺乏
C．受惊吓
D．钙缺乏
E．锌缺乏
