题目

 Traffic rules help to keep order on the road. They also help to keep people  1 . The pedestrian (行人) has as many rules to  2  as the driver of a car. You should wall on the sidewalk (人行道) or at the side of the road. Always look  3  before you wall across the street. If you like riding a bike, don't ride in the middle of the road or run  4  red traffic lights. Whenyou ride a bike with a friend, don't look around or tall. Ifyou drive a car, you should  5  at the traffic lights. You must always  6  a seat belt (安全带). Without belts  7  the driver and the passengers m如图，在直角坐标平面内，函数（x＞0，m是常数）的图象经过A（1，4），B（a，b），其中a＞1．过点A作x轴垂线，垂足为C，过点B作y轴垂线，垂足为D，连接AD，DC，CB．（1）若△ABD的面积为4，求点B的坐标；（2）求证：DC∥AB；（3）当AD=BC时，求直线AB的函数解析式．