How did Masaccio enhance the look of the fresco above?

I just took the test the answer is b. He illuminated the figures from outside light sources.

Masachio whose birth names are Tomasso Di Ser Giovanni di Simone, was a Italian artist. He is known as a great Italian painter of the Quattrocento period of the Italian Renaissance.

In his Fresno work, he painted using a high contrast, he also illuminated the figures from outer light sources and he painted Jesus in lighter colors than the other figures.