We would like to determine if there is acausalrelationship between the thickness of the packaging material and the shelf life of the cheese; that is, does a change in the thickness of the packaging materialcausea change in the shelf life of the cheese?

Select the study that would bebestsource of evidence for establishing the existence of a causal relationship.

Select one:

a.A study which uses a stratified random sample, stratifying by type of cheese, to select units of cheese in the factory and determine the thickness of the packaging material and test the shelf life of each unit.

b.A study which uses a cluster sample, clustering by room the cheese is stored in, to select units of cheese in the factory and determine the thickness of the packaging material and test the shelf life of each unit.

c.A study in which a regression modely=0+1xy=0+1xis estimated from a simple random sample of cheeses from the dairy factory with packaging material thickness (xx) and measured shelf lives (yy) and all necessary assumptions are verified to testH0:1=0H0:1=0againstHA:10HA:10.

d.A study which randomly assigns units of cheese to be packaged with packaging materials of differing thicknesses and then measures the shelf life.