OG #1

[tim60288]

1. The Glass House Mountains in Queensland, Australia,
were sighted in 1770 by the English navigator Captain
James Cook, by whom they were named supposedly
because its sheer wet rocks glistened like glass.

(A) by whom they were named supposedly
because its
(B) by whom they were named supposedly and their
(C) naming them supposedly since their
(D) who so named them supposedly because their
(E) who so named it since supposedly their

Regarding the answer (C), not really understand the explanation from OG below, please help !!
As the object of a preposition and not the subject of the clause, James Cook does not work as the noun that the verbal phrase beginning with naming can describe; the preposition since loses the important causal logic of the sentence.

[shah.abhilash]

hi,

(A) by whom they were named supposedly
because ITS--WRONG(Glass House Mountains is plural,you cant refer with ITS)
(B) by whom they were named supposedly and their-WRONG(use of and is unnecessary,moreover it's a passive sentence(named by))
(C) naming them supposedly since their-WRONG(naming them is wrong here,this whole event has occurred in the past,we cant use a present tense word here. it means to say the mountains were sighted in 1770 by captain James Cook which resulted in the mountains name. WRONG MODIFIER)
(D) who so named them supposedly because their-POTENTIAL ANSWER
(E) who so named it since supposedly their(WRONG)use of it

So D is the answer.

hope this helps to clear your doubt.