Natural Chinese

一： 十一，一个人，….

usage：

一+measure word：When 一 is followed by a forth-tone character, 一 is usually pronounced as second tone, for example: 一个 , 一次.

in other cases, 一 is pronounced as fourth tone, for example: 一杯，一张，一种，一瓶，一把，一直, ….