Suppose a random sample of 50 measurements is selected from a population with a mean of 55 and a variance of 400. Select the pair that is the mean and standard error of x.

a)[55, 2.928]

b)[55, 2.828]

c)[55, 3.028]

d)[50, 2.928]

e)[55, 3.128]

f)None of the above