How about reducing the a mount of water we use every day?

Câu1 : How about reducing the a mount of water we use  every day? 
》Why
Câu2: Why don't you install a burglar alarm in your house ?
》 I suggest
Câu 3: She studies very hard. She passes the exam
》If
Câu 4: What about going out this evening
》 Let't
Câu 5: We keep our environment clean we live a happier àd healthier life
》 If
Câu6: Mr.Phong is busy today . He won't go to work
》...........so........