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.

方程组$\left\{\begin{array}{c}x+y=1\\ y+z=2\\ z+x=3\end{array}\right.$的解是____ 

将一根圆木锯成3段要12分，再将每段平分成两份，还要（　　）分钟．