I chose (E) escaped… was comparable to.
My logic was: the discovery of radium wasn’t what people had imagined (= beyond imagination), and it became so expensive that it was comparable to the rarest gemstone.
For correct answer D) enflamed…exceeded, “exceed” makes sense to me, but “enflame” doesn’t. I thought “enflame” means “to excite an action or a feeling”. And while a discovery is exciting indeed, I think it makes more sense for it to be “beyond imagination” than to “excite imagination”?
We shouldn’t be thinking like “Hmmm - I wonder what the discovery of radium would make people think"?”