Mark the letter A, B, C or D to indicate the word(s) that best completes each unfinished sentence

Mark the letter A, B, C or D to indicate the word(s) that best completes each unfinished sentence.
1. Parents often advise their children not to break the….. of Vietnam’s society in choosing their clothes.
A. principle B. norm C. ability D. form
2. Passengers _____ stop when they meet red traffic light. It is the rule
A. have to B. must C. should D. ought
3. You ………. To talk to your grandparents more often so that you can understand them better.
A. should B. ought to C. ought D. shouldn’t