用英文语法be supposed to 写一篇中国的礼仪习惯

1 You are supposed to shake hands when you meet people for the first time.
2 You are supposed to knock at the door before entering people's houses.
3 You are not supposed to shout or speak loudly in public places.
4 You are supposed to bring a small gift when you are invited as a guest,but the gift is not supposed to be too valuable.