The other day, my brother drove his car down the street at ____ I thought was a dangerous speed. (2

题目

The other day, my brother drove his car down the street at ____ I thought was a dangerous speed. (2
求高手,给出答案,并解释at后面的结构,尤其是thought的宾语和was的主语难道就是一个关联词吗,万分感谢
大家的答案似乎偏离了我要问的啊，再求高手，谢谢

答案

what "那一天,我兄弟开着他的车以一个我认为危险的速度从街上驶过"
at 后面跟宾语,所以用what在这引导一个宾语从句,what在从句"I thought.."里"thought"的宾语.关于was,这里其实是另一个从句,（that）was a dangerous speed.,先行词是what,关系词that代替what在该从句中做主语.