The correct answer is B.
First of all, sustainability consists on the maintenance of a specific behaviour indefinitely.
Environmental sustainability consists on the worlwide generalization of an explotation model with guarantees the preservation of natural resources in the long-term. This involves the adoption of behaviours which are friendly to the environment from the smallest to the largest spheres: in our everyday lives (for example by recycling), change in the type of energies employed, business models, governmental policies (substitute the use of coal or oil by renewable resources).