roles in groups

例句：

1. 1. The president has many roles to play in the meeting.
   总统在会议中有多重角色要扮演。
2. 2. The teacher is responsible for assigning and grading homework.
   老师负责分配和批改作业。
3. 3. Each person has a unique role in the team.
   每个人在团队中都有独特的角色。