Which of the following condition of airway is classified by 'Cotton's grading system'?

The Myer-Cotton grading system describes the severity of stenosis according to the percentage of subglottic stenosis present. The percentage is calculated by measuring the largest sized endotracheal tube that can be passed through the subglottis and comparing this with the age-appropriate tube size for the child. A subglottic diameter of 4 mm in a full-term neonate is considered to be abnormal. Classification From To Grade I No obstruction 50% obstruction Grade II 51% obstruction 70% obstruction Grade III 71% obstruction 99% obstruction Grade IV No detectable lumen