The correct answer is D. Stratified sampling.
Stratified sampling is a probability sampling method in which the population is divided into groups (strata) based on one or more characteristics. Then, a sample is selected from each stratum. This method is more appropriate than other methods when the population is heterogeneous, because it ensures that all groups in the population are represented in the sample.
Sequential sampling is a non-probability sampling method in which the sample is selected one at a time, and the sampling process continues until the desired sample size is reached. This method is not appropriate when the population is heterogeneous, because it is possible that the sample will not be representative of the population.
Quota sampling is a non-probability sampling method in which the sample is selected to ensure that the sample represents the population in terms of certain characteristics, such as age, gender, and race. This method is not appropriate when the population is heterogeneous, because it is possible that the sample will not be representative of the population on other characteristics.
Double sampling is a probability sampling method in which two samples are selected from the population. The first sample is used to estimate the population mean, and the second sample is used to estimate the variance of the population. This method is not appropriate when the population is heterogeneous, because the first sample may not be representative of the population on all characteristics.