I think it doesn't matter whether the stones were found naturally or not What important is the depiction on those stones. in E: if there was a common repertory of mosaic designs with which artisans who lived in various parts of the Roman Empire were familiar, then artisans from Sepphoris could creat...

C seems right. At least it explains how scientists cannot find any physical evidence.

Its D. A seems right. But in the passage, the low level of immune system is compared with the high or normal one. So the measuring of higher or normal immune system is invalid.