Need help with the following questions please:

Khalad is conducting a study to determine if motivational posters inspire middle school students to be more prosocial and to complete more homework. He goes to a large school district to conduct his study. In one of the district's middle schools he puts the posters up and in the second school he does not. After the posters are up for two months he compares the GPA and number of disciplinary referrals between the two schools. Which of the following designs is most representative of Khalad's study?

A. Posttest-only design with nonequivalent groups

B. 2 2 factorial design

C. Posttest-only control group design

D. Solomon four-group design

PJ conducts an experimental study on the effects of soft music during high stakes science testing. He randomly assigns students at the school. In one condition he does not provide music for testing while in the other group he does provide the music. One concern in his study is that during the year the music teacher at the school he administered the study shared with students the physiological benefits of soft music. The introduction of the benefits of music during the duration of his study can be considered which of the following threats?

A. History

B. Mortality

C. Maturation

D. Testing

Kari wants to make sure that all students in her study receive both of the treatments she is testing. To ensure all subjects receive both interventions, which of the following designs should Kari consider?

A. Solomon four-group design

B. Nonequivalent groups control group design

C. Time-series design

D. Counterbalanced design