Those selected as committee members will attend the meeting
那这个句子来说.有一个原则你需要记住,一个句子不管多么长,结构必须是 主+谓+宾.而且谓语只有一个（除非你用and链接）.就是这里的will attend.主语可以是一堆人,宾语也可以是一堆.但谓语动词就一个.所以如果selected用了被动语态（was selected）,那么就存在两个谓语了.
其实可以这么理解这句话,拆开：
1. they are selected as members
2. they will attend meeting