Kelvin: Hi! Dave.
Dave: Hey Kelvin! Why you don’t turn off the lights in your room?
Kevin: I’m just going out to buy something and then I will back to turn off.
Dave: I think you should turn off the power first.
Kelvin: Why?
Dave: Because it helps to save energy. Are you remember? We have pay for electricity is very expensive on last month.
Kelvin: Oh….yes! So that I think I go back to turn off the lights in my room.
Dave: That great!