Choice A is faulty because an adverb such as "twice" cannot function as an object of the preposition "by". B distorts the sentence's meaning,stating that the number of engineering degrees conferred increased on more than two distinct occasions. D's passive verb "was...doubled" suggests without warrant that some unnamed agent increased the number of engineering degrees. The past perfect tense in E,"had...doubled", is inappropriate unless the increase in engineering degrees is specifically being viewed as having occurred further back in the past than some subsequent event. Choice C is best.