根据首字母提示补全短文。

    This is Lin’s first long (1) t______ by train. His brother, Jin told him not to forget where he came

from. Lin (2) n______, unable to speak. He (3) h______ Jin in his arms. With (4) t______ in his eyes,

Jin pushed Lin away. Lin jumped onto the train and found a young man was sitting (5) i______ his seat.

The young man was (6) w______ jeans and a very smart jacket, and was smoking a (7) c______. The

young man would get (8) o______ the train at Hangzhou. At first, he didn’t agreed to (9) m______. But

with the help of a man (10) w______ glasses, Lin got back his seat in the end．

轨道衡常用的限位装置有几种？对限位装置的要求是什么？