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将are very important改为is very important。
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S5. Though a study of this chapter is no substitute for training in public speaking, we believe that its recommendations can nevertheless be of substantial assistance to those who use this book on the numerous occasions when they will be called upon to present their ideas in person before a small group or a large audience.
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S2. In creating a lens a lens designer attempts to trap light by forcing all the rays arising from a single point in the subject to focus on a single point in the image, as a consequence of their passing through a series of transparent (透明的) elements with precisely curved surfaces.
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