21. ______rise in carbon dioxide is causing _______ steady increase in global warming.
A. The; a B.不填; a C. The;不填 D.A；the
22. - Jerry, sorry to have kept you wait.
- It doesn’t matter, but I ________ you ________ later than me.
A. didn’t think, would be B. am thinking, will be
C. thought, had been D. never thought, would be
