I need help with this.

4) The Minneapolis school district implemented an experimental new curriculum designed to improve results on middle school exit exams. Eighth grade classrooms throughout the city were randomly placed into either the control (no change in curriculum) or treatment (experimental curriculum) group at the beginning of the school year. During the first week of classes all students took the exit exam. Then, during the school year instruction in each classroom was prescribed by the randomization process, and the exit exam was administered again at the end of the year. The difference-in-differences diagram below illustrates experimental results. Treatment Test Scores Time a) 0n the figure above draw and/or label the following (label using the number below): 1) The preperiod difference in outcome. 2) The expected post-period outcome for the treatment group (hint: this is the null hypothesis) 3) The effect of the new curriculum on test scores. b) What is the broad trend (across both groups) in test scores between the pre and post period course of the year? Provide at least one possible explanation for this trend. c) Did the new curriculum impact test scores? In what direction?| d) Do you believe the experimental design is internally valid? Why or why not