The correct answer is B. Stratified sampling.
Stratified sampling is a sampling method in which the population is divided into smaller groups, or strata, based on one or more characteristics. A sample is then selected from each stratum in proportion to the size of the stratum in the population. This method ensures that all groups in the population are represented in the sample.
Cluster sampling is a sampling method in which the population is divided into groups, or clusters, and a random sample of clusters is selected. All individuals in the selected clusters are then included in the sample. This method is often used when it is difficult or expensive to obtain a list of all individuals in the population.
Convenient sampling is a sampling method in which individuals are selected for the sample based on their convenience to the researcher. This method is not a reliable way to obtain a representative sample of the population.
Lottery method is a sampling method in which individuals are selected for the sample by chance. This method is also not a reliable way to obtain a representative sample of the population.
Stratified sampling is the most suitable sampling method when a research problem is related to heterogeneous population because it ensures that all groups in the population are represented in the sample. This is important because it allows the researcher to make inferences about the entire population based on the sample.