It is so cold that you can’t go outside _____ fully covered in thick clothes.
| A．if | B．unless |
| C．once | D．when |
32. I ____ what he said, but I don’t _____ him.
| A．believe, believe in | B．trust, believe | C．believe in, credit | D．depend on, believe in |
31. Do you know when did the world _____?
| A．come into being | B．come | C．formed | D．Existed |
30. The coal we use today should _____ plants and trees.
| A．begin with | B．start with | C．commence as | D．originate as |
29. That's all for the party. Let's _____.
| A．fall asleep | B．go to sleep | C．go to bed | D．be asleep |
28. They ____ friends since they met in Shanghai ten years ago.
| A．have become | B．have turned | C．have been | D．have grown |