What Does Sustainability Mean for Low Energy Buildings

What does sustainability mean for low energy buildings?

A) All windows have low emissivity glass
B) Brick, steel and concrete walls save more energy consumption while in use than they cost to produce and construct
C) Aluminium window frames are not used in this building
D) Double glazed windows always used in cold climates
E) All thermal insulation, glass, aluminium, steel, timber and concrete in this building were harvested from renewable resources