真空断路器以（）作为灭弧介质。

A.空气

B.氩气

C.氮气

D.真空

根据句意及汉语提示,写出各单词的正确形式,每空填一词.

1. The camera was one of the great ________ in the second half of the 19th century. (发明)

2. Some people are good at ________, but they never give back. (借)

3. With the _______ of modern medicine, many difficult illness can be cured and prevented.(发展)

4. Everyone was very generous and they had lots of support from local b________. (企业)

5. They are so weak that they can't walk any ________. (远)