​Which statement is true of body mass index? (a) ​It correlates with disease risks. (b) ​It decreases by 1 unit for every 10 years of life. (c) ​It provides an estimate of the fat level of the body. (d) ​It is defined as the person's height divided by the square of the weight. (e) ​Its absolute value is less important than the rate at which it changes.