这个戏剧由三个人物组成的三重奏推动情节发展。

The play's plot is driven by a ___triad of characters.

警方正在调查一个涉嫌走私的三合会组织。

The police are investigating a ___triad suspected of smuggling.

在音乐课上，老师教我们如何构建一个大三和弦。

In music class, the teacher showed us how to build a major ___triad.