在线等~~~急急急~~~答案是128m/s怎么做~~~？？

A student makes measurements from which she calculates the speed of an object to be 127.66 m s-1. She estimates that her result is accurate to ± 2%. Which of the following gives her result expressed to the appropriate number of significant figures?
大家请注意，这道题的答案是128m/s
主要问题是，我不知道为什么~~~