在关系代数中,下列哪一个等式是不正确的
A.
B.R∪S=S∪R
C.R×S=S×R
D.
参考答案:A
溶液、胶体和浊液这三种分散系的根本区别是 [ ]
A.能否透过滤纸
B.能否发生丁达尔效应
C.是否均一、透明、稳定
D.分散质粒子的大小
— Why do we get up so early?
— If we ______ the flight we would have to stay here for another day.
A.will miss
B.miss
C.missed
D.would miss