Please choose the correct ending to complete the given sentence: Health: [header] How to use an ophthalmoscope [title] Determine if the ophthalmoscope is working properly. [step] Turn the power switch to the on position to check if the light works. If not, replace the batteries and try again.

Ending1: Look through the aperture (eyepiece) to ensure clarity. Remove or slide open the aperture's cover if one exists. Ending2: If the light plays on and/or makes noises, then the ophthalmoscope is functioning properly. It may be necessary to replace the batteries if there are still noises or light is still flickering. Ending3: [substeps] If the light does not click on, this indicates that the light is dead and unusable. [title] Clean the lens using a lens wipe. Ending4: If it is not working, replace the batteries and make sure the aperture is not too large. If the aperture seems too small, dial the power switch.

Answer format: ending1/ending2/ending3/ending4