An international agricultural research group wants to compare a new variety of corn ("Variety B") with a widely-used standard (called "Variety A"). Ten countries participate in the study and each country assigns two one-acre plots to the study. The plots within country are randomly assigned so that one plot receives variety A and one plot receives variety B. After the harvest, corn yield is measured for each plot.

1. Is this an experiment or an observational study? Justify your answer.

2. Was there a control or comparison group in this study? If so, describe how this is implemented. If not, briefly discuss a potential problem due to lack of a control or comparison group in the study.

3. Was randomization incorporated in this study? If so, discuss how randomization was incorporated. If not, briefly discuss a potential problem due to lack of randomization in the study.

4. Was replication incorporated in this study? If so, discuss how replication was incorporated. If not, briefly discuss a potential problem due to lack of replication in the study.

5. If the results are statistically significant, can we conclude causation (i.e. that variety of corn used affects the yield)? Justify your answer.