The following passage needs stronger development. Opening paragraph: A science passage explains a threshold effect in a water-filtration system. Development paragraph: The author writes, "A gradual increase in input can produce an abrupt change once a system's capacity is exceeded." A specific case should appear next. The following paragraph says the threshold should be estimated from repeated observations, not one dramatic event. Which sentence belongs in the blank while remaining precise enough for the passage's scope? The revision must fit both the abstract claim and the development that follows.