A:(1,2)
B:(2,1)
C:(1,2)或(2,-1)
D:(2,1)或(-1,2)
Food safety is very important. Rules must be made to____.
张籍的《贾客乐》:“金陵向西贾客多,船中生长乐风波。……金多众中为上客,夜夜算缗眠独迟。”姚合《庄居野行》:“客行野田间,比屋皆闭户。借向屋中人,尽去作商贾”。唐人的这些诗句,反映了