The producer is the tree which means that C is the right answer. The tree is known to be vital for a lot of living things. It has the ability to produce oxygen. This is needed by living things so that they can breathe. The moment that there is not enough oxygen available in the world, living things might die. Trees can also serve as the shelter of different animals. There are even human beings that create tree houses.
The tree house can be the place where kids can hang out or it can also be the place where adults can relax. It will depend on how the tree will be used. It is obvious that the tree has a lot of uses.