The other day my brother drove his car down the street at I thought was a dangerous speed

问题补充：

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

A. as

B. which

C. where

D. what

答案：

A. as

B. which

C. where

(答案→)D. what

解析：考查宾语从句，此题考查作介词at的宾语从句，I thought为插入语，所以从句中就缺少了主语，故用关系词what，几天前我的哥哥在大街上行驶，以一种我认为是非常危险的速度。故选D。