A public health researcher wants to study the prevalence of a certain disease in a large city.. To ensure they have a representative sample, they divide the city into different regions based on socioecon omic status (low,middle, and high income). Then , they randomly select a proportion al number of individuals from each socioeconc mic group to participate in the study. Which type of sampling technique is being used in this scenario? a. Simple Random Sampling b. Stratified Sampling c. S ystematic Sampling d. Cluster Sampling