EX 1 :

1 I visited Bana Hills last summer .

2 They went skiing three months ago .

3 Nam is doing homework at the moment .

EX 2 : 

1 I like the living room best in my house .

2 How about going to Sa Huynh Coffee tonight ?

3 You mustn't talk too much in the class .

Nước cứng là nước có cha nhiều các cation nào sau đây?

A. Na + ,   K +

B.  Ca 2 + ,   Mg 2 +

C.  Li + ,   Na +

D.  Li + ,   K +