Nowadays people take___ exercise a day as they did in the past because of widely used automobiles.   

A．less than half

B．less than as half as

C．less than half as much

D．half less than

针对学龄前儿童的口腔预防措施是

A．对儿童和老师进行健康教育
B．群体应用氟泡沫和氟保护漆
C．龋齿充填和非创伤性充填
D．含氟牙膏刷牙与控制甜食
E．群体应用氟离子导人措施