1.Adults are not willing to say hello.
2.School went from impersonal to personal,and that resulted in more class participation and better grades.
3.saying hello to each other/ greeting each other/ saying hello
4.①lowering blood pressure ②relieving stress ③boosting happiness
5.不管出于什么原因,我在城里打招呼得到的回应比在乡村少得多.
答案不唯一