9. Techniques to employ the energy of the sun are being developed.
A. convert
B. store
C. use
D. receive
10. Since the Great Depression， the United States government has protected farmers from damaging drops in grain prices.
A. slight
B. surprising
C. sudden
D. harmful
11. Cement was seldom used in building the Middle Ages.
A. crudely
B. rarely
C. originally
D. occasionally
12. Medicine depends on other fields for basic information， particularly some of their specialized branches.
A. conventionally
B. obviously
C. especially
D. inevitably
13. We were astonished to hear that their football team had won the champion.
A. amazed
B. amounted
C. amused
D. approached
14. There is an abundant supply of cheap labor in this country.
A. a steady
B. a plentiful
C. an extra
D. a stable
15. The most crucial problem any economic system faces is how to use its scarce resources.
A. puzzling
B. difficult
C. terrifying
D. urgent