When the birth rate is equal to each woman producing exactly enough offspring to replace herself and her offspring’s father, and the birth rate is sustained for a generation, then..

C) reflection (i also looked up the other choices just to make sure)

1.wear safety goggles when heating or mixing substances 2.tie back long hair when doing experiment in order to prevent from catching fire or dipping into chemicals accidentally 3.keep all exits and passages clear4.wear laboratory coats