Sustainable living is a lifestyle adopted by individuals or societies which is geared towards reducing the consumption of earths natural resources. The idea is to lower the carbon footprint by switching to sustainable modes of transport, living spaces, food consumption etc.
In the given passage, the sentences that describe sustainable living are:
1) 'I plan to buy a hybrid for better gas mileage': Since a hybrid is a combination of a petrol engine and an electric motor, it reduces the consumption of fuel and is more energy efficient.
2) 'I am able to carpool with a couple of friends from work' : Carpooling reduces the vehicles on road thereby reducing vehicle exhaust.
3) 'The architects received a LEED certification': LEED certified buildings are energy efficient constructions.