Final answer:
The nurse concludes that the reason the healthcare provider selected a specific antibiotic is due to the sensitivity of the bacteria.
Step-by-step explanation:
The reason the healthcare provider selected a specific antibiotic for the toddler with cystic fibrosis and bacterial pneumonia is because of the sensitivity of the bacteria. The healthcare provider likely identified the specific bacteria causing the pneumonia and chose an antibiotic that is effective against that particular strain. Sensitivity testing can help determine which antibiotics will be most effective in treating the infection.