In the following essay, each blank has four choices. Choose the best answer and writedown 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 wavesmust be relayed by means of "dishes" or (30) . These can be installed on towers, highbuildings, and mountain tops.

（26）是（）

A.optical

B.radio

C.electrical

D.magnetic

Ⅰ. 土建工程
某建筑物部分图纸内容如图3-2所示。
[问题]

现浇钢筋混凝土雨篷的强度等级为C20(石子＜20mm)，现场拌制，雨篷翻檐高度为120mm，混凝土保护层厚度为25mm，计算雨篷的清单工程量。