"In which" MUST be followed by a location?! HELP ME PLZZZZ

Like can we say “a process in which”!!! Process isn’t a place :S I don’t know how is this C!!!: In developing a method for writing the Cherokee language, Sequoyah used a system (where each spoken syllabe) is represented by a different symbol.
A)As it is
B)used a system of which each spoken syllable
C)used a system in which each spoken syllable
D)using a system each spoken syllable of which
E)using a system of which each spoken syllable
seems to me that ALL including C is wrong because what I know is that in which must be followed by a place and is used just as “when”. System is NOT a place :S??!!!