心肺复苏胸外心脏按压与口对口呼吸的比例是（）
参考答案：30：2。
下列物质中，属于氧化物的是（ ）
A．O2
B．P2O5
C．KOH
D．CuSO4
A good teacher should encourage his students to ____ the knowledge by themselves instead of just copying and memorizing what the teacher said in class.
A．expand
B．observe
C．digest
D．react
