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 |
相关试题
Bad habits, ____formed, are difficult, and sometimes impossible to shake off.
| A．once | B．before | C．until | D．unless |
Only when you leave your parents for college education _______ how much you love them.
| A．do you realize | B．you realize | C．you will realize | D．will you realize |
The cause he had devoted himself to _______ a perfect success.
| A．proving | B．proved | C．was proved | D．has been proved |
Many experts believe that teachers’ development is _____ the key to better education lies. 
| A．that | B．what | C．where | D．which |
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