A:士别三日,刮目相看
B:仁者见仁,智者见智
C:因地制宜,因时制宜
D:金无足赤,人无完人
①三个氢氧根离子____②干冰____ ③汞元素____.
(a·b)·7=____·(____·____)
— Oh, I as ill as I do now for a long time.
二年级有6排座位,每排坐7个同学。一共可以坐几个同学?