This is stated in the passage, but this is not the main point. Instead, this information supports the author’s main point that that antique windows are not thicker at the bottom because of the downward flow of glass.

This is stated in the passage but this is not the main point. This information explains why we see varying thickness in antique glass but not in modern glass. The information in (B) serves to support the author’s claim that the variations in window thickness are not due to gradual downward flow of glass.

While the passage references a new study that calculated the time needed for viscous flow to change the thickness of glass, the passage only mentions this calculation as it relates to types of glass, not solids in general. Additionally, the reason the author mentions this research is to debunk a previous belief––the research itself is not the main point; the research supports the main point.

Anti-supported. In fact, the author claims that this downward flow is not a factor that contributes to the differences in thickness in old windows. It would take many trillions of years for downward flow to change the thickness of glass, and medieval cathedrals are only a few hundred years old.

This is the main point. The author debunks the commonly held belief that the flowing of solid glass causes difference in thickness in old windows. The author then goes on to suggest an alternative hypothesis: that it’s actually manufacturing techniques that caused these differences.