When you are _______ about which button to press on the complicated machine, you can either read the user’s guide for guidance or fax us for specific instruction. Don’t ______ the trial-and-error method.

　 A. insure; do　 B. ensure; make　 C. uncertain; try　 D. unsure; touch

    I must have been about fourteen then, and I put away the incident from my mind with the
easy carelessness of  youth. But the words, Carl Walter spoke that day, came back to me years
later, and ever since have been of great value to me.
Carl Walter was my piano teacher. During one of my lessons he asked how much practicing I was doing. I said three or four hours a day.
"Do you practice in long stretches, an hour at a time?"
"I try to."
"Well, don't," he exclaimed. "When you grow up, time won't come in long stretches.    Practice in minutes, whenever you can find them five or ten before school, after lunch, between household tasks. Spread the practice through the day, and piano-playing will become a part of your life."
When I was teaching at Columbia, I wanted to write, but class periods, theme-reading, and committee meetings filled my days and evenings. For two years I got practically nothing down on paper, and my excuse was that I had no time. Then I remembered what Carl Walter had said. During the next week I conducted an experiment. Whenever I had five minutes unoccupied, I sat down and wrote a hundred words or so. To my astonishment, at the end of the week I had a rather large manuscript ready for revision, later on I wrote novels by the same piecemeal method. Though my teaching schedule had become heavier than ever, in every day there were idle moments which could be caught and put to use. I even took up piano--playing again, finding that the small intervals of the day provided sufficient time for both writing and piano practice.
There is an important trick in this time--using formula: you must get into your work quickly. If you have but five minutes for writing, you can't afford to waste four chewing your pencil. You must make your mental preparations beforehand, and concentrate on your task almost instantly when the time comes. Fortunately, rapid concentration is easier than most of us realize.
I admit I have never learnt how to let go easily at the end of the five or ten minutes. But life can be counted on to supply interruptions. Carl Walter has had a tremendous influence on my life. To him I owe the discovery that even very short periods of time add up to all useful hours I need, if I plunge（投入）in without delay.
56．The meaning of “stretch” in the underlined part is the same as that in sentence “       ”.
A．The forests in the north of the province stretch for hundreds of miles.
B．Bob worked as a government official for a stretch of over twenty years.
C．My family wasn’t wealthy by any stretch of the imagination.
D．During his senior year his earnings far enough to buy an old car.
57．Which of the following statements is true?
　　A．The writer didn’t completely take the teacher’s words to heart at first.
　　B．Carl Walter has had a great influence on the writer's life since he became a student.
　　C．The writer owes great thanks to his teacher for teaching him to work in long stretches.
　　D．Rapid concentration is actually more difficult than most people imagine.
58．We can infer that the writer             . 
A．has new books published each year however busy his teaching is
B．is always tired of interruptions in life because his teaching schedule is always heavy
C．has formed a bad habit of chewing a pencil while writing his novels
D．can find sufficient time for mental preparations beforehand, so he's devoted to work   instantly
59．What is the best title of this passage?
A．Concentrate on Your Work           B．A Little at a Time
C．How I Became a Writer                 D．Good AdviceIs Most Valuable