Within a small chamber, an internal combustion engine combines a precisely measured mix of fuel (typically petrol or diesel) and air. Once ignited, this explosive combination causes an expansion of hot, pressurized gases to exit the chamber, typically via pistons or a turbine. Thus the chemical energy is converted, albeit often not very efficiently, into mechanical energy which can then be used to power motors and drive machines.
the word or the verb smiling is in present tense then the word or the noun everyone is plural so since your verb is in present tense you will use ARE and you can use WERE if your verb is in past tense.