because vs since

[tankobe]

The Five Langang Lakes were sighted in 1600 by Stenphen, who they were named supposedly because its shapes look like circles.
(D) who so named them supposedly because their
(E) who so named it since supposedly their

this is a sentense foundamentally revised from a OG question. the OG said since,in this context, is different from because, so E is wrong. Really? if so, what is the difference?
(i know E is wrong because of "it" and the wrong place of 'supposedly' although OG did not mention the issue)

[natalie]

Hey Stephen, here's the link of explanation from Stacy, which explained "since v.s because" since-vs-because-t3206.html


Natalie

[RonPurewal]

in that choice (e), "it" is very clearly incorrect (because "lakes" is plural). therefore, there's little reason to dig into subtleties on that particular choice.