Question

Why is bamboo considered one of the best renewable resources on the planet?

Answer 1

can be used as food as well as construction material.
It can grow in any tropical region in the world.
It grows quickly and in dense conditions.
It is an extremely hard substance that can be used to make furniture as well as bridges.

Answer 2

Bamboo can be harvested in about 5 years.
Other trees like oak need about 40 years to mature.
It also grows in a great variety of conditions.

So i think your third answer is correct.
It grows quickly and in dense condition.