What do art historians regard as the real subject of Monet's Rouen Cathedral: The Portal ( in Sun ) ?

A) French religious history
B) The sunlight on the portal
C) A crisis of faith
D) The poverty nearby

Monet's series of paintings focusing on Rouen Cathedral, including "The Portal (in Sun)," is celebrated for its exploration of the effects of light and atmosphere on the cathedral's façade at different times of the day and in different weather conditions. The real subject is the changing light on the portal, not the architectural details or the surrounding context.