A school principle wants to observe if natural light has an effect in the classroom learning. The principle randomly chooses two groups of students of the same age and grade, and places both groups in rooms on opposite sides of the school, one facing east and one facing west, during a 10am class. The test scores of both classes are compared at the end of the semester. How could this observation be changed into a valid experiment of the effects of natural light?
A. by introducing adjustable light fixtures in each classroom
B. by tinting the windows in both classrooms
C. by including classrooms facing north and south
D. by introducing adjustable blinds in each classrooms

Martha has a deck of cards. she has lost some of the cards, and now the deck only contains nine spades, eleven diamonds, eight clubs, and twelve hearts. martha predicts that whenever she draws a card from the deck without looking, she will draw a club one-fifth of the time. which activity would best allow martha to test her prediction? a. randomly draw a card from the box and see if it is a club. b. randomly draw a card. then, continue to draw another card until all eight clubs are drawn. c. randomly draw and replace a card 120 times. then, observe how close to 30 times a club is drawn. d. randomly draw and replace a card 100 times. then, observe how close to 20 times a club is drawn.