A manufacturing company has implemented a continuous improvement program based on the Six Sigma methodology. They are currently analyzing data from their production process and identify a bottleneck causing high defect rates. What should be the NEXT step in their Six Sigma approach?

a$)$ Define the problem statement and set specific improvement goals.

b$)$ Implement pilot solutions on a small scale to test their effectiveness.

c$)$ Train employees on new quality control procedures.

d$)$ Validate the pilot solution's impact on defect rates through statistical analysis.

e$)$ Hold brainstorming sessions to generate ideas for additional root cause analysis.