Answer:
The experiment could be made more valid by:
• Running a pretrial or using existing data from a time when nobody drinks the juice as a baseline.
This option would help establish a baseline productivity level for the workers before introducing the special juice. By comparing the performance of Group A (given the special juice) with the baseline performance, it would be easier to determine whether the special juice indeed had an impact on productivity. This approach helps control for any external factors that may affect productivity, making the experiment more valid and the results more reliable.