读图，有关我国西高东低阶梯地势的有利影响，下列叙述错误的是（    ）

下列物质的用途，主要利用其化学性质的是（ ）

    When I entered Berkeley, I hoped to earn a scholarship (奖学金). Having been a straight-A 1 I believed I could take difficult subjects and really 2 something. One such 3 was World Literature run by Professor Jayne. I was greatly interested in the ideas he 4 in class.

    When I took the first exam, I was 5 to find a 77, "C+", on my test paper. I went to Professor Jayne, who 6 my arguments but remained 7 I decided to try 8 although I didn't know what that 9 because schooling had always been easy for me. I read the books more 10, but got another 77. Again, I reasoned (争论) with Professor Jayne.11 he listened patiently but wouldn't 12 his mind. One more test before the final exam. One more chance to 13 my grade. So I redoubled my14. But my efforts were no good and everything went as 15.

    The last hurdle (障碍) was the final. No matter what grade I got, it wouldn't 16 three "C+". I might as well kiss the scholarship good-bye. I 17 working hard. I felt I knew the course material as well as I ever would. The night before the final, I even 18 myself to a movie. The next day I decided for once I'd have fun with a test. A week later, I was surprised to find I had got a(n) "19". I hurried into Professor Jayne's office. He seemed to be expecting me. "If I gave you the grade as you expected, you wouldn't continue to work as hard."

    It was the 20 "A" on the course. The next year I received my scholarship. I've always remembered Professor Jayne's lesson: you alone must set your own standard of excellence.