有关大陆架和大陆坡的说法，正确的是(　　)

下列表述中，属于“史论”的是（    ）

51453502是____位数，最高位是____位，其中的三个5分别表示____、____、____。

    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.