David Beckham has ________ it takes to become a professional football player.

A．who

B．what

C．which

D．that

It is pretty well understood ________ controls the flow of carbon dioxide in and out the atmosphere today.
A．that B. when C. what D. how

After three hours'climbing，they reached ________ they thought was the place they'd been dreaming of.

A．what

B．which

C．where

D．that

________ has been mentioned above，continued chairman after he took a sip of coffee，________ the project must be carried out before spring flood comes.
A．As；that B. That；which
B．This；which   D. It；that

There is a common belief among them ________ rubbish can and should be put to good use.

A．which

B．if

C．whose

D．that