What significant change took place in the Abbey Church of Saint-Denis?

a.

The tower was changed.

b.

The stained glass windows were replaced with new ones.

c.

Three portals were added to the western facade.

d.

all of the above

I think the correct answer from the choices listed above is option D, all of the above. The significant changes that took place in the Abbey Church of Saint-Denis were tower was changed, the stained glass windows were replaced with new ones, three portals were added to the western facade.