请问下列三个句子表达上正确吗？有没语法错误

1,定语从句,需要有代词形式,someting不适用,需要改成what
2,happen 作vi,happen to + sb
没有"to"the meeting 这种用法,改成"on"或者"at"the meeting ,表示在"会议中"
3,to改成at/on, 这样陈述没有语法错误,但是太累赘,建议用""tell sb sth(定语从句)"形式

建议改写成:
She failed to tell him what happened at the meeting.

1.She failed to tell him something happened on the meeting?
改为:She failed to tell him what had happened at the meeting.这样时态和语法才对.后两句也不对,只能改成这句子.

3错了