Write the next sentence in the following story.

How to sterilize water with sunlight
Clean the bottle.
Remove anything in the bottle like dirt and on the bottle like a label. This method works with pet bottles (the clear/uncolored plastic bottles often used for mineral water or soft drinks and soda) and certain kinds of glass bottles.

OPT:
1). Remember to rinse, soap, and water off thoroughly in a glass clean water storage container. If the label says that it says that it's " water safe " or " sterile, " use it to wipe off the label of either the bottle or your pet bottle.;
2). Again, dry clean the bottle if it has old plastic bottles, or small bowls to fill with oil or solvents. ( clean bottles should not be on plastic).;
3). The use of pet bottles for this process has been researched and found to be safe when used correctly. Because not all types of glass allow for the transmission of uv rays, pet is often recommended over glass, especially since plastic bottles are also less breakable and cheaper.;
4). The water container that holds the container will also be sterilized. Fill a cup or container with water and 3/4 cup (120 ml) of white vinegar.;. The answer should be
3).