Which Patient Assessment Indicates the Most Severe Respiratory Distress

Which patient assessment indicates the most severe respiratory distress?

A) Nasal flaring,symmetrical chest wall expansion,SaO₂ 88%
B) Abdominal breathing,SaO₂ 97%
C) Substernal retraction,SaO₂ 84%
D) Substernal retraction,SaO₂ 90%