68. Eventually， people spread throughout the continent， ______ the entire species.
A. wiping out
B. wiping away
C. wiping off
D. wiping up
69. Experts say walking is one of the best ways for a person to ______ healthy.
A. preserve
B. stay
C. maintain
D. reserve
70. Faced with the ______ difficulties， they are determined to carry on their program.
A. satisfactory
B. attributable
C. innocent
D. intangible
71. Fewer and fewer of today's workers expect to spend their working lives in the same field， ______ the same company.
A. all else
B. much worse
C. let alone
D. less likely
72. Flying in an airplane was once thought to be an impossible ______.
A. task
B. profession
C. promise
D. contest
73. Fresh vegetables are straight from the ______ and raw vegetables are ______.
A. earth……cooked
B. soil……uncooked
C. floor……cooked
D. ground……uncooked
74. From this material we can _____ hundreds of what you may call direct products.
A. derive
B. discern
C. diminish
D. displace