题目内容：
In the ginseng trial the researchers tested the potency of ginseng__________
A．that led the researchers in Duke’S School of Nursing to study it B．by giving different dose of the herb to patients with different cancers
C．whether the foods and supplements patients took every day were good or not
D．though both flaxseed and ginseng are all healthy alternative medicines
E．that either of them iS benefieial to cancer patients
F．because we still have to see if flaxseed can prevent prostate cancer
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