Which of the given hypotheses are constructed correctly?

1. If the same object is weighed on the Earth and the Moon, then it will weigh less on the Moon because gravity affects the weight of an object.
2. If a balloon is taken high up in the air, its volume will increase.
3. If a candle requires oxygen to continue burning, then the candle's flame will go out.
4. If plants require carbon dioxide to grow and a plant is placed in a room without carbon dioxide, then the plant will not grow.

Select the correctly constructed hypotheses.