Manufacturers Were Subdivided into Groups by Volume of Sales

Multiple Choice

Manufacturers were subdivided into groups by volume of sales.Those with more than $100 million in sales were classified as Class A large;those from $50 to $100 million as Class A medium size;and those between $25 and $50 million... ,and so on.Samples were then selected from each of these groups.What is this type of sampling called?

A) Simple random
B) Stratified random
C) Cluster
D) Systematic