百日咳痉咳期的治疗原则是：（ ）
A．清肺涤痰
B．泻肺镇咳
C．泻火涤痰
D．宣肺止咳
E．敛肺止咳
参考答案：B
下列物质对应的化学式不正确的是
A．氧化镁-MgO
B．石灰水-Ca(OH)2
C．氧气-O
D．氧化铜-CuO
It is about 600 years ago ______ the first clock was made.[ ]
A. that
B. until
C. before
D. when
