The correct answer is A. iid.
An iid (independent and identically distributed) random variable is a random variable that is independent of all other random variables in the sample and has the same distribution as every other random variable in the sample.
A random sample is a set of data points that are selected from a population in such a way that each data point has an equal chance of being selected.
The default model for random samples is an iid random variable. This means that each data point in the sample is assumed to be independent of all other data points in the sample and to have the same distribution as every other data point in the sample.
The other options are not correct because they do not meet the definition of an iid random variable.
B. id (independent) random variables are random variables that are independent of each other, but they do not have to have the same distribution.
C. pmd (population mean distribution) random variables are random variables that have the same distribution as the population mean.
D. all of the mentioned is not correct because it includes options that are not correct.