The correct answer is: B. Distribution free statistics
Distribution free statistics are statistics that do not depend on the distribution of the population. This means that they can be used to estimate parameters of a population even if the distribution of the population is unknown.
Option A, selected statistics, is incorrect because selected statistics are statistics that are calculated from a sample that has been selected from a population. The selection of the sample may or may not specify any conditions about the parameter of the population.
Option C, census, is incorrect because a census is a survey of the entire population. A census is not a sample, and therefore it cannot be used to estimate parameters of a population.
Option D, none of the above, is incorrect because distribution free statistics are a type of statistic.