Explanation:

- Statement (1): "Seed" is the keyword here; elephants play a crucial role in dispersing seeds across the ecosystems they inhabit.

- Statement (2): The sentence suggests that the subject leads to a lack of young growth, implying the absence of an important animal.

- Statement (3): This word should signify young plants or trees that grow from the seeds.

- Statement (4): Pertains to those species whose seed dispersal entirely depends on elephants.

- Statement (5): Points out the adaptability and problem-solving abilities of elephants, enhancing their impact on the ecosystem.

- Option 1, engineers: Though elephants are described as engineers of the ecosystem, this doesn't fit the context of absence in forests.

- Option 2, elephants: Correct Answer: This fits perfectly as elephants are vital for seed dispersal, leading to young plant growth.

- Option 3, conservation: Not suitable in the context of absence affecting young plants.

- Option 4, seeds: As the primary focus is on the absence impacting growth, it doesn’t fit logically here.