用can,must,musn't,haveto,hasto填空
Doyouunderstandalltheseroad-sighs?Lookatthetrafficlights.Theyarered.You_________stopyourcar.Now,theyaregreen,you________moveon.Thereisasignwith"NOPARKING".You_________leaveyourcarthere.You________parkyourcarintherightplace.Adriver__________learntrafficruleswell.He________getadriver'slicense.