Consider the following statements of Odum regarding the conditions that maintain biological energy flow in estuaries and choose the correct answer:
1. Tidal action that maintains a rapid removal of waste products of metabolism
2. A variety of plant species and life-forms that provide a continuous photosynthetic process
3. An estuary often functions as a nutrient trap
4. Close contact between autotrophic and heterotrophic layers

A. Only 1, 2 and 3 are true

B. Only 2, 3 and 4 are true

C. Only 2 and 3 are true

D. 1, 2, 3 and 4 are true

Answer: Option D