Please choose the correct ending to complete the given sentence: Health: [header] How to prevent tooth enamel erosion [title] Brush your teeth twice a day. [step] In order to keep your teeth healthy, it is important to brush your teeth regularly. Brushing your teeth removes a wide variety of substances that are bad for your teeth, including sugary and acidic foods that can eat away at your tooth enamel.

Ending1: Brushing this way will ensure that any food that ends up in your mouth is removed. As a general rule of thumb, brush your teeth once or twice a day. Ending2: Most dentists recommend brushing your teeth twice a day for about 20 minutes. The more frequently you brush your teeth, the better your overall health is. Ending3: [substeps] Wait to brush your teeth until at least 30 minutes after meals. Acidic foods that you eat can weaken tooth enamel, which can lead to damaging the enamel when brushing. Ending4: If you are between age 60 and 65, no more than twice a day should be used for three months. Long-term brushing may have a negative effect on enamel.

Answer format: ending1/ending2/ending3/ending4