Consider the following statements and choose the correct answer:
1. The ecosystem is a major ecological unit
2. The function of ecosystem is related to the flow of energy and the cycling of materials through the structural components of the ecosystem
3. The major functional unit of the ecosystem is the population
4. The ecosystem has historical aspects: the present is related to the past, and the future is related to the present

A. 1, 2, 3 and 4 are true

B. Only 2 and 4 are true

C. Only 1 and 3 are true

D. Only 1, 3 and 4 are true

Answer: Option A