investigating a process requires investigating every stage of the process & scientists want to investigate the water cycle & a cycle is a kind of process ->  scientists have to investigate every stage of the water cycle  scientists have to investigate every stage of the water cycle & precipitation is a stage in the water cycle process ->  scientists have to investigate precipitation in the water cycle  scientists have to investigate precipitation in the water cycle & investigating something requires investigating the properties of something ->  scientists have to investigate the properties of percipitation  scientists have to investigate the properties of percipitation & the amount of precipitation is a property of precipitation & investigating sometimes requires measuring -> scientists have to meausre the amount of precipitation