Karl marx believed that society is divided into what two classes?

The answer is the bourgeoisie class and the proletariat class.

Explanation:  The bourgeoisie class are the capitalists that owns the means of production in a society while the  proletariat class are the working class who sell their labour power.

Marx argued that the bourgeoisie exploited the proletariat. The proletariat was made to do more jobs which created more wealth for the bourgeoisie. He noticed that the work carried out by the proletariat created large wealth for the bourgeoisie. The products produced in the factory  were sold for more than the value of the labour itself i.e. more than the workers' wages. That means the working class earn less.

answer:

d. because dr. laguardia selected a widely used measure, his study generalizes to has strong external validity. external validity has limited external validity. other applications of this measure.

the widely used measure that he applied to his experiment was the benton facial recognition test. it employed on to football players and as result, only players who suffered brain concussions did not pas this test. and although it has an external validity, it is limited because it isn't general to apply to other population.