Introduction:
There are various things in the world that require both water and air to fulfill their needs. In this case, a moving sailboat and a seed growing into a plant are two such examples. Let's understand why these options require both water and air.

Explanation:
A moving sailboat:
- A sailboat is a type of watercraft that uses wind to propel itself through the water.
- To move, a sailboat relies on the force of the wind acting on its sails, which then generates the necessary energy to push the boat forward.
- In order for the wind to exert force on the sails, it requires an unobstructed path through the air.
- Additionally, the wind also needs water to create the necessary pressure differentials that allow for the generation of wind.
- Therefore, a moving sailboat needs both air for the wind and water for the boat to move.

Seed growing into a plant:
- When a seed is planted in soil, it requires both water and air to grow into a plant.
- Water is essential for the germination process, where the seed absorbs water and begins to sprout.
- The presence of air is crucial for the seed's respiration, as it requires oxygen to carry out cellular respiration and produce energy.
- Without oxygen, the seed would not be able to sustain its cellular functions and ultimately die.
- Additionally, air also plays a role in the exchange of carbon dioxide, allowing the plant to release waste gases produced during respiration.
- Therefore, a seed growing into a plant requires both water for germination and air for respiration.

Conclusion:
In conclusion, both a moving sailboat and a seed growing into a plant require both water and air to fulfill their needs. The sailboat needs air for wind propulsion and water to generate wind, while the seed needs water for germination and air for respiration. Both of these examples highlight the importance of water and air in different aspects of life.