To Test the Effect of an Informal Atmosphere on Class

To test the effect of an informal atmosphere on class performance, Professor Hall dresses in shorts and bare feet for his morning class and in conventional clothing for his afternoon class. He then counts the number of "intelligent questions" in each class and reports more in the class for which he wore shorts. What are the two things wrong with this experiment?

A) lack of random assignment and lack of blind observations
B) differential survival and lack of an independent variable
C) lack of blind observations and lack of a dependent variable
D) lack of random assignment and lack of an independent variable