Please choose the correct ending to complete the given sentence: Travel: [header] How to fly a hot air balloon [title] Understand why a balloon rises. [step] Hot air balloons are based on a simple concept. As you heat air, or any other gas, it becomes less dense.

Ending1: If you make up your own self-heating plan, your balloon will not rise. [title] Understand how air stays in your balloon. Ending2: Just like a bubble rising in an aquarium, the hot air will float above the denser, colder air around it. Get the air in the balloon hot enough, and it can lift the balloon canvas, the basket, and everyone inside it as well. Ending3: When a balloon is short and lightweight, it helps the air hold in the balloon but is able to capture more gas for maximum efficiency. These gases can exist as long as the oxygen is below it. Ending4: An average balloon is about the same shape as a golf ball but it has large, round feet and no other internal components. The upper tires are more dense, and gases are produced when sweat flows through between the tires.

Answer format: ending1/ending2/ending3/ending4