21. Higher temperatures turning the large ice sheet to water would cause_____ rise in sea level worldwide and change_____ weather on earth.
A. a; / B. the; /
C. a; the D. /; the
22. —The woman biologist stayed in Africa studying wild animals for 13 years before she returned!
—Oh, my God! She_____ a lot of difficulties.
A. may have gone through
B. might go through
C. ought to have gone through
D. must have gone through。
