下列生殖方式中属于无性生殖的是（　　）

A．试管婴儿

B．蚕蛾的卵孵出幼虫

C．鸡卵孵出小鸡

D．嫁接的板栗

In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.

Microwave communication uses (1) -frequency radio waves that travel in straightline sthrough the air. Because the waves cannot (2) with the curvature of the earth, they can be (3) only over short distance. Thus, microwave is a good (4) for sending data between buildings in a city or on a large college campus. For longer distances, the waves must be relayed by means of" dishes" or (5) . These can be installed on towers, highbuildings, and mountain tops.

1（）

A．high

B．low

C．long

D．short