Assume that the duration of human pregnancies can be described by a Normal model with mean 266 days and standard deviation 13 days. a) What percentage of pregnancies should last between 271 and 282 days? b) At least how many days should the longest 25% of all pregnancies last? c) Suppose a certain obstetrician is currently providing prenatal care to 51 pregnant patients. Let y represent the mean length of their pregnancies. According to the Central Limit Theorem, what is the distribution of this sample mean, y? Specify the model, mean, and standard deviation. d) What's the probability that the mean duration of these patients' pregnancies will be less than 255 days? a) The percentage of pregnancies that should last between 271 and 282 days is %. (Round to two decimal places as needed.) b) The longest 25% of all pregnancies should last at least (Round to one decimal place as needed.) days. c) Select the correct choice below and, if necessary, fill in the answer box(es) within your choice. OA. A Binomial model with trials and a probability of success of (Type integers or decimals rounded to two decimal places as needed.) OB. A Normal model with mean and standard deviation (Type integers or decimals rounded to two decimal places as needed.) OC. There is no model that fits this distribution. d) The probability that the mean duration of these patients' pregnancies will be less than 255 days is (Round to four decimal places as needed.)