A certain mental development index for infants is a standardized measure used in observing infants over time. It is approximately normal with a mean of 105 and a standard deviation of 15. Complete parts a through d. a. Find the z-score corresponding to the upper quartile (Q3) of a normal distribution. The z-score that corresponds to the upper quartile (Q3) of a normal distribution is 0.67. (Round to two decimal places as needed.) b. Find and interpret the lower quartile and upper quartile of the mental development index. Interpret the lower quartile. Select the correct choice below and fill in the answer box to complete your choice. (Round to one decimal place as needed.) O A. Twenty-five percent of infants score lower than O B. Twenty-five percent of infants score higher than O c. The percentage of infants that score below 25 is %. O D. The percentage of infants that score below 75 is %