Naturally occurring chemicals cannot be newly patented once their structures have been published. Before a naturally occurring chemical compound can be used as a drug, however, it must be put through the same rigorous testing program as any synthetic compound,cuminating in a published report detailing the chemical's structure and observed effects. if the statement above are true, which of the following must be also true on the basis of them ? A,B,C很好排除，关键是D和E D)once a naturally occurring compound has been approved for use as a drug, it can no longer be newly patented. E)a naturally occurring chemical cannot be patented unless its effectiveness as a drug has been rigorously established 答案选D,我觉得E更合适，为什么选D呢？ | 
