What Was the Major Point Learned in the 1991 Biosphere

Multiple Choice

What was the major point learned in the 1991 Biosphere 2 experiment?

A) We should focus on recycling waste and wastewater.
B) We should learn how to grow a rainforest in an enclosed area to life-support.
C) We must be aware that CO₂ recycling is really difficult.
D) We cannot engineer life-supporting systems as well as those provided by nature.
E) We must admit that extinction is inevitable.