Answer:
C. It was impossible for her to be in the same room with him with the windows closed.
Step-by-step explanation:
In this sentence, we learn that Gregor's sister, Grete, is afraid of Gregor. We learn that when she walks into Gregor's room, she feels the need to open the window and breathe. She does so even when opening the window causes them discomfort. It is clear to Gregor that Grete is too scared to be able to be in the same room as him with the windows closed.