地铁

Ths yars you can s many undrground railways ar bing built in som big citis. undrground railway is both convnint and fast. th undrground railway is also calld th tub,th subwayor th undrground. Thrr lifts for you to go up or down. th trains doors opn and clos automatically. in shanghai, during rush hours th undrground arrivs at th station vry two minuts. But with too many popl taking th undrground, popl find it rally too crowdd. mayb shanghai nds mor undrground railways.