Whenever you see a long sentence with lots of commas, try to find the most important grammatical parts of the sentence. For instance, the clause starting with "due to" is superfluous. What's left is, "Whereas automobile buyers cannot easily compare..., so they cannot."
With its short underlined portion, this question is testing idioms. Since the word following the comma is "so," you should recall the idiom "Just as..., so...." Choice (B) begins with "Just as," and it is correct.