Answer:
C)
Step-by-step explanation:
In sentences 1-2, the answer is clear: "(1) College classrooms are often drab and dreary places. (2) Walls are painted a variation of “institutional gray”" etc. as well as sentence 8: "8) The control classroom, which they called the “sterile classroom,” had white walls, a gray carpet, and rows of plastic desks."
The walls are white, therefore the answer is C.