A:How soo
B:How old
C:How ofte
D:How long
As I joined the big crowd, I got________from my friends.
水是生命之源,也是人类宝贵的资源.生活中可以用____鉴别硬水和软水;饮用硬度过大的水不利于人体健康.因此人们常采用的____ 方法将硬水软化.