Geologists recently discovered that the stress placed by gravity on the fabric of the sand interlocks the particles in sediments
which, in turn, forms structures that are majestic and resilient, such as the Delicate Arch in Utah’s Arches National Park.
In GMAT - usage of which(without a comma) to modify noun is not correct. Also, here which is modifying the action - the stress... interlocks the particles .... - incorrect. So, Option A and E can be ruled out.
In C : to form, in turn, structures that are majestic and resilient
the stress placed by gravity on the fabric of the sand interlocks the particles in sediments to form, in turn, structures that are ...
it seems that the stress itself make the structures - incorrect
B. that forms majestic and resilient structures in turn - placement of modifier 'in turn' changes the meaning - incorrect
D. that, in turn, form majestic and resilient structures
the stress placed by gravity on the fabric of the sand interlocks the particles in sediments
that, in turn, form majestic and resilient structures, such as the Delicate Arch in Utah’s Arches National Park.
Usage of that clause to refer to action ; Placement of modifier - in turn; and such as following the structure - all are correct.
Answer D