Please choose the correct ending to complete the given sentence: Health: [header] How to test nitric oxide levels [title] Buy nitric oxide test strips. [step] There are several brands of commercially-available test strips that measure the levels of nitric oxide found in the saliva. These levels are supposed to indicate how much circulatory nitric oxide is being produced in your body.

Ending1: Check with your doctor before using one of these, as its reliability will vary from brand to brand. [substeps] Nitric oxide test strips can be purchased directly from your manufacturer. Ending2: Read the label carefully so you know how much nitric oxide you will be taking. Based on the product and the testing site, you may have several dozen different test strips available to you. Ending3: Purchase these strips online, or at select pharmacies and health stores. [title] Place the test strip on your tongue for 5 seconds. Ending4: [substeps] The nitric oxide test strips come in every color of the rainbow (including red, brown and yellow). Most have a shorter screen, so there is space between the test strips.

Answer format: ending1/ending2/ending3/ending4