For another subject (a 29-year-old male) in the study by Diskin et al. (A-11), acetone levels were normally distributed with a mean of 870 and a standard deviation of 211 ppb. Find the probability that on a given day the subject’s acetone level is:

(a) Between 600 and 1000 ppb

(b) Over 900 ppb

(c) Under 500 ppb

(d) Between 900 and 1100 ppb