Identify the requirements for a discrete probability distribution. Choose the correct answer below. A. There must be a fixed number of independent trials. There must be two mutually exclusive outcomes for each trial with a constant probability of success. B. The sum of the probabilities must equal one. C. The sum of the probabilities must equal one. Each probability must be between zero and one inclusive. D. Each probability must be between zero and one inclusive.

Afactory makes propeller drive shafts for ships. a quality assurance engineer at the factory needs to estimate the true mean length of the shafts. she randomly selects four drive shafts made at the factory, measures their lengths, and finds their sample mean to be 1000 mm. the lengths are known to follow a normal distribution whose standard deviation is 2 mm. calculate a 95% confidence interval for the true mean length of the shafts. input your answers for the margin of error, lower bound, and upper bound.