Explanation

Creating a filter: the original sentence has a verb error. The grammatical subject corresponding to the verb "were" is "passion," which is grammatically singular. "Music," "philosophy," and "fields" are nouns but are within the prepositional phrase beginning with "of," so they cannot be the grammatical subject. We can start by filtering on that error.

Applying the filter: based on the filter, we eliminate (A) and (E). We'll narrow down (B), (C) and (D) on other grounds.

Finding objective defects: choice (B) uses the phrase "as well as," and that phrase doesn't convey the intended meaning correctly. The "as well as" doesn't fit because, idiomatically, we describe influence in terms of degree or amount (how much it influenced) and in terms of quality (whether it did a good job of influencing). Choice (D) is grammatically legal but distorts the intended meaning. Without the word "as," the latter phrase is descriptive. With the "as," it's giving a reason. So it seems to be saying, "Why was Jobs' passion for humanities critical to his success? Because it influenced his design the same amount as his technological savvy did." That's sensible but off base, because in the intended sense the latter portion is an elaboration of the main point, not a condition for it. The correct answer is (C).