Imagine an argument for the conclusion that the dust storms in Oklahoma in the 1930s were caused by over-plowing. If that argument were based on the authority of statements made by documentarian Ken Burns (and you were going to put the argument into the form of a statistical syllogism as we did) which of the following would be a premise in that argument?

a. Ken Burns is an interested party since he's paid to make claims about the dust bowl.

b. "Dust storms in Oklahoma in the 1930s were caused by over-plowing" is something said by Ken Burns about dust storms in Oklahoma in the 1930s.

c. 90% of the grassland in the Oklahoma panhandle had been plowed for wheat.

d. Ken Burns is an expert on dust storms in Oklahoma in the 1930s.