Researchers want to investigate if students retain more information if it printed on blue paper rather than white paper.They recruit 100 elementary students, 100 middle school students, and 100 high school students to participate.The researchers then randomly assigned half of the elementary students, half of the middle school students, and half of the high school students to receive the information on blue paper.The remaining students receive the same information on white paper.Which of the following best describes this experimental design?

a) Block design with grade of student as the blocks.

b) Stratified design with color of paper as the blocks

c) Block design with color of paper as the blocks

d) Stratified design with grade of student as the blocks

e) Completely randomized design