Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions from 21 to 25.

The Old Woman and the Doctor

An old woman became almost totally blind from a disease of the eyes. After consulting a doctor, she made an agreement with him in the presence of witnesses that she would pay him a high fee if he cured her. However, if he failed, he would receive nothing. The doctor prescribed a course of treatment and visited her on a regular basis to apply ointment to her eyes. With each visit, he took away with him some article from the house, until at last, when he visited her for the last time and the cure was complete, there was nothing left. When the old woman saw that the house was empty, she refused to pay him his fee. After repeated refusals on her part, he sued her before the magistrates for payment of her debt. On being brought into court, she was ready with her defense. "The claimant," she said, "has stated the facts about our agreement correctly. I promised to pay him a fee if he cured me, and he, on his part, promised to charge nothing if he failed. Now, he says I am cured; but I say that I am blinder than ever, and I can prove what I say. When my eyes were bad, I could see well enough to know that my house contained a certain amount of furniture and other things. But now, when according to him I am cured, I am entirely unable to see anything there at all."

Why did the woman refuse to pay the doctor?

Cold temperatures, short growing seasons, and heavy snows prevent ________ at high elevations.