Excellent!
OA is E.
OE:
Spot the Error:
Descriptive phrases set off at the beginning or end of the sentence indicates a modifier being tested.
Rule and Fix:
A Modifier must be as close as possible to the thing it describes.
POE:
Since the modifier is valid as given keep A and eliminate any choice that improperly alters that modifying phrase. (Eliminate B and C)
Chunk and Compare:
Compare A to C.
Choice A uses which instead of that.
Rule: Use which as part of a phrase that is set off by commas and can be removed from the sentence without changing the meaning.
Which is not used properly in this case so eliminate A.
Compare the remaining choices or look for another error.
Alarm: Comparisons
Rule: Items compared must be logically and structurally parallel
Compare D to E.
Choice D incorrectly compares a drop vs. year and choice E correctly compares drop vs. drop, since the statement that of refers to the drop in that year.
Reread your choice:
Choose E