Use the Following to Answer the Questions

Use the following to answer the questions.
Because of the development of optical scanners and cable television,marketing researchers can now test the effectiveness of advertising more precisely.Volunteers in a minimum of six cities are offered food discounts in return for allowing marketing research firms to monitor grocery purchases and send trial commercials to their homes through cable television.
The research subjects shop only at stores equipped with UPC scanners,and their purchases are identified by a special card.Respondents are also told that some of the commercials they see on cable television may differ from those seen by their neighbors.Buying patterns are then compared.For example,Kashi cereals tested a Crunchy Wheat promotion using this system.Half of the 5,000 participating homes in one city saw a commercial announcing the promotion; the other half saw a commercial that did not mention the promotion.Kashi used scanner data to evaluate the promotion's success and offered the commercials nationwide.
-Refer to Scenario 4.1.Suppose that when selecting the 5,000 homes to participate in scanner studies in one city,the research firm first divided the city's population into upper-,middle-,and lower-class families,then took a probability sample within each group.This would be a(n) ____ sample.

A) random
B) stratified
C) area
D) quota
E) population