Here is my idea why i did not choose A in the beginning. In GMAT, most of time "that" has to directly refer to the nouns in front of it. However, there is no noun in front of "that" and thus "that" here will not refer to "reasons."
Sure, there are examples such as "reasons of.... and that of..." in OG, but the "that" is close enough and parrellel enough and will never follow the first idea after so many words.
but the second half, i can not find a verb: a surge in the economy to a 5.6 percent annual growth rate and improved corporate earnings balanced by the lack of signs of inflationary pressure.