During BOD analysis, why is it critical that the 300-mL glass BOD bottle be completely filled with the liquid sample, leaving absolutely no headspace or air bubbles?

• To prevent the glass bottle from shattering due to gas pressure buildup
• To ensure the dissolved oxygen probe fits tightly without leaking
• To create an anaerobic environment necessary for rapid bacterial respiration
• To prevent atmospheric oxygen from dissolving into the sample and skewing the BOD result