The federal rules aimed at protecting human subjects of medical experiments were established to ensure that patients must be warned of potential risks and an independent panel would evaluate the experiment before it was conducted.
must be warned of potential risks and an independent panel would
must be warned of potential risks and that an independent panel
are warned about potential risks and that an independent panel
will be warned about potential risks and an independent panel would
would be warned of potential risks and that an independent panel would
choice a,b: ensure和must是赘余的
因为主句的谓语动词were established 已经限定发生在过去,从句中的谓语动词也要补出助动词would
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