Only three strategies are available for controlling cancer: prevention, screening and treatment. Lung cancer causes more deaths than any other types of cancer. A major cause of the disease is not (21) known; there is no good evidence that screening is much helpful, and treatment (22) in about 90 percent of all cases. At present, therefore, the main strategy must be (23) . This may not always be true, of course, as for some other types of cancer, research (24) the past few decades has produced (or suggested) some importance in prevention, screening or treatment.
(25) , however, we consider not what research may one day offer but what today’s knowledge could already deliver that is not being delivered, then the most practicable and cost-effective opportunities for (26) . premature death from cancer, especially lung cancer, probably involve neither screening nor improved (27) , but prevention.
This conc
A. if
B. unless
C. provided
D. while
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