A researcher wants to investigate the impact of salt water on the growth of plants. Which of the following would be the best hypothesis for this experiment?

A) If salt water is used to water plants, then the plants will not grow as tall as those watered with tap water.`

B) Plants need water to grow, and they should also be exposed to sunlight.

C) I think salt water will help plants grow taller.

D) I will add salt water to plants and observe how they grow.