吸食毒品对人体的危害是    （     ）

    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.

    Bob and Sue are in the same school，1they are in different classes.After school，Bob and Sue often play games with their friends.Class begins at eight in the morning.Now Bob and Sue are in2own classrooms.They are3to their teachers.Bob is studying English.Sue is having an art lesson.She4to make a birthday card5her mother.

    Her teacher Miss Li is helping her.