A.A
B.B
C.C
D.D

函数上有（）。

若f(x)在x=a某邻域内有定义，且存在，则f(x)在x=a处（）。

Like fine food, good writing is something we approach with pleasure and enjoy from the first taste to the last. And good writers, like good cooks, do not suddenly appear full-blown. Quite the contrary, just as the cook has to undergo an intensive training, mastering the skills of his trade, the writer must sit at his desk and devote long hours to achieving a style in his writing, whatever its purpose—school work, matters of business, or purely social communication. You may be sure that the more painstaking the effort, the more effective the writing, and the more rewarding.

There are still some remote places in the world where you might find a public scribe to do your business or social writing for you, for a fee. There are a few managers who are lucky enough to have the service of that rare kind of secretary who can take care of all sorts of letter writing with no more than a quick note to work from. But for most of us, if there is any writing to be done, we have to do it ourselves.

We have to write school papers, business papers or home papers. We are constantly called on to put words to paper. It would be difficult to count the number of such words, messages, letters, and reports put into the mails or delivered by hand, but the daily figure must be enormous. What is more, everyone who writes expects, or at least hopes, that his writing will be read. We want to arouse (引起) and hold the interest of the readers. We want whatever we write to be read, from first word to last, not just thrown into some "letters-to-be-read" file or into a wastepaper basket. This is the reason we bend our efforts toward learning and practicing the skills of interesting, effective writing.

正确

错误

Sometimes, people (41) your life and you realize that they are there (42) some purpose, to (43) you a lesson, or to help you (44) who you are or who you want to become. You’d never know who these people (45) be, your friend, your classmate, your neighbor, your co-worker, your teacher, or (46) a stranger, but they will deeply (47) your life in some way.

And sometimes things (48) to you that may seem (49) , painful and horrible at first, but (50) , you realize that without (51) those difficulties you would never know your strength, (52) or potential. Everything happens for a (53) . Nothing happens by (54) or by means of good luck. Illness, great achievement, love, injury and failure all come to (55) the limits of your soul. Without these tests, life would be like a straight and fiat road, but it goes (56) . It would be safe and comfortable, but dull and completely (57) .

Those people who affect your life, and the failure and the success you experience can help you to create who you are and who you become. Even the bad experiences can (58) from. In fact, they are the most important ones. If someone breaks your heart, or hurts you, please (59) them, for they helped you to learn about the importance of being careful when you open your heart. If someone loves you, love them (60) , because they are teaching you to love and how to open your heart and eyes to things.

函数在x=1点可导，则（）。