concentrate on：集中在；专心于
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They had a deadline every one or two months to aim at when the next minor grading would take place.
aim at：瞄准；指望；目的在于
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用心书写你的人生 Write Your Own Life
戴维·A.伯曼/David A. Berman
Suppose someone gave you a pen-a sealed, solid-colored pen. You couldn't see how much ink it had. It might run dry after the first few tentative words or last just long enough to create a masterpiece (or several) that would last forever and make a difference in the scheme of things. You don't know before you begin.