【推荐1】John tried hard to figure out ______ he has left his schoolbag but in vain.

A．what

B．which

C．where

D．that

【推荐2】A large number of young women, unconscious that they are at risk, live in _____ UNAIDS calls “challenging environments”, with insufficient access to food and education.

A．where

B．what

C．why

D．how

【推荐3】The other day, my brother drove his car down the street at _____ I thought was a dangerous speed.

A．as	B．which
C．what	D．that