For his science project, austin wants to determine if the ph of standing rainwater changes over time. he collects rainwater and distributes it evenly in 5 jars and places them all indoors in a spot that does not receive a lot of sunlight to limit evaporation. using a ph testing kit, he measures the ph of the water in the first jar on the 4th day, second jar on the 8th day, third jar on the 12th day, fourth jar on the 16th day and fifth jar on the 20th day. what is the independent, or manipulated, variable in austin’s experiment? a the number of days the rainwater is allowed to sit b the amount of sunlight c the change in the amount of rainwater due to evaporation d the change in ph of the rainwater over time