The lengths of a particular animal's pregnancies are approximately normally distributed, with mean muequals265 days and standard deviation sigmaequals12 days. (a) What proportion of pregnancies lasts more than 274 days?(b) What proportion of pregnancies lasts between 259 and 271 days? (c) What is the probability that a randomly selected pregnancy lasts no more than 253 days?(d) A "very preterm" baby is one whose gestation period is less than 235 days. Are very preterm babies unusual?