我国原始社会结束在（     ）

甲                          乙

mouse和cloud中的ou发音相同。

    There have been many comparisons (比较) made between London Underground and New York Subway. They are the best known public transport systems (公共交通运输系统) in the world and each is a key part of one of the greatest cities of the world. The two systems have many things in common(相同), including their ages and fame（名声）, but there are also important differences.

    The following table shows some of the similarities (类似）and differences.

手持一个凸透镜在室内白墙和窗户之间移动（离墙更近些），在墙上能看到（　　）