单项选择题

According to the author, clinical trials of vitamin supplements______.

A．often result in misleading conclusions
B．take time and will not produce conclusive results
C．should be conducted by scientists on a larger scale
D．appear to be a sheer waste of time and resources
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单项选择题
At one time doctors discouraged taking multivitamins because they believed that multivitamins______.
A．could not easily be absorbed by the human body
B．were potentially harmful to people's health
C．were too expensive for daily consumption
D．could not provide any cure for vitamin deficiencies
单项选择题
It has been found that vitamin E______.
A．should be taken by patients regularly and persistently
B．can effectively reduce the recurrence of heart disease
C．has a preventive but not curative effect on heart disease
D．should be given to patients with heart disease as early as possible
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