A．onceB．neverC．sometimeD．over and over
A. once
B. never
C. sometime
D. over and over
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British scientists' demonstration implies that ______.
A. single cancer genes are harmless
B. the development of cancer is a complex process
C. a carcinogenic chemical is required for cancer to develop
D. cancer genes can cause cancer only in conjunction with a carcinogen
Compared with wage cost, the non-wage cost differences in EC countries are much more likely to ______.
A. increase dramatically
B. decline sharply
C. fluctuate intermittently
D. disappear gradually
Cells injected with a single cancer gene ______.
A. were unaffected completely under such circumstances
B. only occasionally developed cancer
C. developed tumor but not cancer
D. were changed but did not become malignant
This passage is mainly concerned with ______.
A. the definition and classification of intellectual property fights
B. the difference between copyrights and industrial property
C. the reasons for protecting intellectual property rights
D. the social objectives of intellectual property rights
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