The passage most helps to answer which one of the following questions?

I don't understand the timeline expressed in the answer choice with that laid out in the passage To elaborate, I was dead set on B at first. But what deterred me was where the passage says, "Until the nineteenth century, the only way to make window glass was to...". This lead me to assume that this practice changed/modernized in the 19th century, further leading me to conclude that the shift in practice made during the 19th century is parallel with the practice performed today. Although incorrect based on the correct answer choice (B), if this were the case, it wouldn't explain how today's practice differ from those of the 19c but with earlier centuries (>18c) The following shows how I saw/interpreted the timeline in my mind: X-1700s/18c: blow molten glass into a large globe and then flatten into disk ~1800s/19c: new method comes about or, in other words, the modern approach (19c-21c) --> Therefore, this does not explicitly state how 19c techniques differ from those used today but rather how >18c practices differ from today What I'm looking to understand is the timeline and/or where we are lead to believe in the passage that the techniques used in the 19c differ from today