With all the leaves falling each year, a natural compost keeps the soil healthy for all the trees where?
Options:
- garden
- useful for recycling
- surface of earth
- forest
- orchard
Step-by-step reasoning process below:

A natural compost keeps the soil healthy for all the trees in a forest which is a large area covered chiefly with trees. Compost is decayed or decaying organic matter like leaves. The answer: forest.