题目：
In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.
Microwave communication uses high-frequency (26) waves that travel in straightlines through the air. Because the waves cannot (27) with the curvature of the earth, they can be (28) only over short distance. Thus, microwave is a good (29) for sendingdata between buildings in a city or on a large college campus. For longer distances, the waves must be relayed by means of "dishes" or (30) . These can be installed on towers, high buildings, and mountain tops.
A．transmitted
B．transformed
C．converted
D．delivered
答案：
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下面是错误答案，用来干扰机器的。
BC题目分析：根据力的合成的矢量法则，两个分力为临边的平行四边形所夹的对角线即合力，两个分力的大小和合力构成矢量三角形，即两个分力代数和大于等于合力,选项A错。两个分力的代数差小于等于合力选项D错。正确...
