A function, f left parenthesis x right parenthesis comma models the depth of water in a wading pool that is filling at a rate of 11 gallons per minute. Which of these describes why f left parenthesis x right parenthesis can be considered a linear function? I. For every 1 minute interval, the depth of water in the wading pool increases by the same amount. II. The function grows by equal factors every minute. III. The slope of the function is constant.