Read the following passage and answer the questions that follow:

doctor pascal
by emile zola

in the heat of the glowing july afternoon, the room, with blinds carefully closed, was full of a great calm. from the three windows, through the cracks of the old wooden shutters, came only a few scattered sunbeams which, in the midst of the obscurity, made a soft brightness that bathed surrounding objects in a diffused and tender light. it was cool here in comparison with the overpowering heat that was felt outside, under the fierce rays of the sun that blazed upon the front of the house.

standing before the press which faced the windows, dr. pascal was looking for a paper that he had come in search of. with doors wide open, this immense press of carved oak, adorned with strong and handsome mountings of metal, dating from the last century, displayed within its capacious depths an extraordinary collection of papers and manuscripts of all sorts, piled up in confusion and filling every shelf to overflowing. for more than thirty years the doctor had thrown into it every page he wrote, from brief notes to the complete texts of his great works on heredity. thus it was that his searches here were not always easy. he rummaged patiently among the papers, and when he at last found the one he was looking for, he smiled.

for an instant longer he remained near the bookcase, reading the note by a golden sunbeam that came to him from the middle window. he himself, in this dawnlike light, appeared, with his snow-white hair and beard, strong and vigorous; although he was near sixty, his color was so fresh, his features were so finely cut, his eyes were still so clear, and he had so youthful an air that one might have taken him, in his close-fitting, maroon velvet jacket, for a young man with powdered hair.

the use of the phrase "great works on heredity" serves which of these purposes in the passage?

it deepens the physical description of the room.
it foreshadows a problem dr. pascal will face.
it provides a clear indication about dr. pascal's career.
it establishes a somber but serious tone for the story.