介质访问控制协议可划分为3类：
参考答案：
争用协议、无冲突协议和有限争用协议。
Do you know _____ over there? [ ]
A. what happens
B. what was happened
C. what is happening
D. what did happen
下列化学方程式正确的是（ ）
A．2Fe+6HCl═2FeCl3+3H2↑
B．4Fe+3O2 点燃 . 2Fe2O3
C．2KNO3+CaCl═2KCl+Ca（NO3）2
D．2NaOH+SO2═Na2SO3+H2O
