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．optical

B．radio

C．electrical

D．magnetic

女性，35岁，患肺结核已3年，治疗不规则，2天前受凉后发热，T38℃，体检无明显异常，胸片示两上肺片状阴影，伴不规则透亮区，为判断肺结核是否有活动，下列最有意义的是（）.

A.痰结核杆菌阳性

B.胸片上有空洞性病变

C.胸片上浸润性病灶

D.发热等结核中毒症状

E.血沉增高