To provide an airtight seal during mouth to mouth ventilation, in addition to pinching the nostrils, you should:

When administering mouth-to-mouth ventilation, achieving an airtight seal is crucial for ensuring that the air you exhale is effectively delivered into the victim's lungs rather than escaping into the environment. Applying your mouth tightly over the victim's mouth helps create that seal, enabling proper air transfer.

This method prevents any significant leakage of air, thus increasing the effectiveness of the ventilation. When the nostrils are pinched, this further optimizes the ventilation by directing the air solely into the lungs. It’s essential to maintain this tight connection while performing rescue breaths, as a loose contact can result in wasted breaths and compromised effectiveness of the aid being provided.

Other options do not achieve this airtight seal as effectively. For example, using a breathing mask may be appropriate in specific scenarios, especially when available, but relies on external equipment rather than a direct method with just your mouth. Covering the mouth with a cloth could impede the airflow or create an obstruction, while maintaining an open airway with your fingers does not inherently assist in creating the necessary seal that direct mouth-to-mouth contact provides.