南京是国民政府的所在地，抗战期间被日军占领，国民政府不得不迁都，当时作为国民政府

某同学将落在地上的重为1 N 的物理书捡起放到0.8m高的桌面上，在此过程中他至少对书做了多少功？

最易发生脐带脱垂的胎先露是（）

A.完全臀先露

B.肩先露

C.枕先露

D.腿直臀先露

E.不完全臀先露

美的三种形态是（）

A.优美

B.自然美

C.社会美

D.艺术美

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.

4（）

A．material

B．equipment

C．medium

D．channel

什么叫止回阀（H）？