By ____, the national anthem is played at the beginning of a con

By ____, the national anthem is played at the beginning of a concert and at the end of a film.
A、convention
B、tradition
C、norm
D、principle
E、 
【正确答案】：A
【题目解析】：convention 惯例；tradition 传统；norm 规范；principle 原则句意; 按照惯例，国歌在音乐会开始和电影结束时演奏。