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953.   Although no proof yet exists of electromagnetic fields generated by household appliances posing any health threat, mounting scientific evidence has convinced many experts that there is cause for concern.

(A) of electromagnetic fields generated by household appliances posing any health threat

(B) of electromagnetic fields generated by household appliances that pose any threat to health

(C) that electromagnetic fields generated by household appliances pose any threat to health

(D) that poses any threat to health from electromagnetic fields generated by household appliances（C）

(E) for any health threat posed by electromagnetic fields generated by household appliances

that在此的作用是什么？有点不可理解。。。。

搜索无果难道是这个问题过于弱智了? 请高人指点

定语后置

proof （that。。。。） yet exists