透射式幻灯机是根据___原理设计的,即光源发出的光线经聚光镜会聚照亮幻灯片,再通过放映镜头在银幕上形成___的幻灯片图像。
No more having to buy expensive textbooks which you will only use for a year or two and then sell or _______ away.
You can _____ some bottles of wine, or some chocolates, or a bunch of flowers.
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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