Solution

The goal is to find the statement that, if true, weakens the study's conclusion that reducing work hours is beneficial. A weakening statement will introduce a negative consequence or undermine the positive claims.

Analysis of Options:

• A, C, and D all support or strengthen the study's conclusion by highlighting positive outcomes (fewer delays, productivity improvement, higher profits).
  
• B (Employees demanded higher wages): This weakens the conclusion. If reducing hours leads to demands for higher wages, it would increase operational costs. This directly supports the counter-argument mentioned in the passage and makes the practice less beneficial for companies, thus weakening the study's overall positive conclusion.
  

Conclusion:

Statement B is the only one that presents a significant drawback, thereby weakening the argument that reducing work hours is a net positive.