Sentence Correction

School integration plans that involve busing between suburban and central-city areas have contributed, according to a recent study, to significant increases in housing integration, which, in turn, reduces any future need for busing.
(A) significant increases in housing integration, which, in turn, reduces
(B) significant integration increases in housing, which, in turn, reduces
(C) increase housing integration significantly, which, in turn, reduces
(D) increase housing integration significantly, in turn reducing
(E) significantly increase housing integration, which, in turn, reduce


The QA is A. But why? "which" modifies "increases" thats why it must be next to "increases", right?

Here which is refering to housing integration so reduces -OK

thanks