GMAT Sentence Correction (SC) | Re: The remarkable similarity of Thule artifacts throughout a vast region

The remarkable similarity of Thule artifacts throughout a vast region can, in part, be explained as a very rapid movement of people from one end of North America to the other.

(A) The remarkable similarity of Thule artifacts throughout a vast region can, in part, be explained as- "explained as" cannot be used.. we need "explained by" here
(B) Thule artifacts being remarkably similar throughout a vast region, one explanation is - "being" modifies "artifacts"
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