Please choose the correct ending to complete the given sentence: Health: [header] How to get low cost tooth whitening [title] Try whitening strips. [step] Like other over-the-counter treatments, you can buy whitening strips from the store. As their name implies, they are strips that fit over your teeth.

Ending1: [substeps] To use, you cover the front of your teeth with the strips and then leave them on for 30 minutes. You must do this every day for about two weeks. Ending2: They have a long, thin handle that you attach one end of a piece of dental floss to your teeth. They are also designed for use on smoking, by numbing the enamel in your mouth after smoking. Ending3: They are available in either gel or powder form. [substeps] These don't require you to shave. Ending4: They provide a stronger whitening agent that will evenly dry and form teeth, making them convenient for those with sensitive teeth. Taking whitening strips was popular in the mid-30s, with twenty-four glossy and commercially-made strips used to run down the sides and back of gums.

Answer format: ending1/ending2/ending3/ending4