Please choose the correct ending to complete the given sentence: Computers and Electronics: [header] How to weld underwater [title] Identify the site and material of the joint to be welded and clean it. [step] Most underwater welds involve steel, but metals may vary. [title] Prepare a chamber to place around the joint (each joint should have a separate chamber).

Ending1: [step] Much of the sand used during welding will stick to metal, so consider covering the ground with sand if your project requires a flat surface. [title] Waste all the sand that is taken up by the joint. Ending2: [title] Find a weld compound for the joint to rest in and sandpaper those joints which are closely joined to one another for proper welder techniques. [title] Hammer the joints together using 100/200 grit sandpaper. Ending3: [step] Chambers range in size-some are large enough to fit several welder-divers, others are only small enough for the welding electrode. [title] Introduce gas into the chamber and pump out the water. Ending4: [title] Use coarse sand (also also known as regular sand) which should be used sparingly. [step] Sand is mineral grade, free from dirt and grease, making it easier to weld against the cliffs.

Answer format: ending1/ending2/ending3/ending4