Experts are trying to work out a plan to deal with the problems caused by global warming ______ it is too late.
| A．when | B．if | C．before | D．until |
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 |
“What were you trying to prove to the police？” “___ I was last night.”
| A．That | B．When |
| C．Where | D．What |
. Patience is a kind of quality — and that is ___A___ it takes to do anything well.
| A．what | B．which |
| C．which | D．how |
They lost their way in the forest, and _______ made matters worse was that night began to fall.
| A．it | B．which |
| C．that | D．what |
He told me the news, believe it or not, ______ he had earned $1 000 in a single day.
| A．that | B．which |
| C．as | D．because |