A) As compared to western settlement of Greenland,
since the eastern settlement of Greenland lies farther south, is less marginal for Norse hay production, supported more people
, it was thus less at risk of collapse. Wrong comparison. Two ICs not connected using conjunction.
B) As compared to western settlement of Greenland,
since the eastern settlement of Greenland lay farther south, was less marginal for Norse hay production, supported more people, it was thus less at risk of collapse. Same error as A
C) Compared to western settlement of Greenland,
eastern settlement of Greenland lay farther south,
was verb1 less marginal for Norse hay production, supported more people, and
was verb2 thus less at risk of collapse. Correct. Verb pair correctly connected using and.
D)
When compared to western settlement of Greenland, the eastern settlement which lies farther south, was less marginal for Norse hay production, supported more people; it was less at risk of collapse.
When compared to is undiomatic
E)
When compared to western settlement of Greenland, because the eastern settlement lay farther south, was less marginal for Norse hay production supported more people; and hence it was less at risk of collapse than the other.
When compared to is undiomatic
Things to remember.
As compared to is correct usage.
When compared to is undiomatic.