Please choose the correct ending to complete the given sentence: Food and Entertaining: [header] How to whiten teeth with hydrogen peroxide [title] Brush with a whitening toothpaste. [step] Purchase a whitening toothpaste with hydrogen peroxide at your local pharmacy or grocery store. Brush with the product at least twice daily for at least one month to see results.

Ending1: [title] Spot test your whitening toothpaste. [step] Look for ingredients that may be too whitening for your mouth or gums. Ending2: Be sure to brush according to the packaging, in order to avoid any irritation. It is important to see the whitening side of the toothpaste (the area that contains the whitening solution), in order to make sure that it is effective. Ending3: [substeps] Do not brush more than twice a day for the first two months to see results. After three months, a pea-sized amount will be enough to achieve whitening. Ending4: [substeps] Buy a product with at least 3.5% hydrogen peroxide, which is the standard amount. Be aware that the more hydrogen peroxide in a product, the likely it is to make your teeth sensitive.

Answer format: ending1/ending2/ending3/ending4