The gas in the piston is being heated, and the piston has moved upward. The observation will be summarized in a row of the incomplete table below.
 Row : 1, 2, 3, 4 
 Name:Boyle's law, Charles’s law, Gay- lussac's law, Combined gas law
 Observation: Volume increases when pressure decreases, ?, ?, ?
 Variables: ?, ?,Temperature, pressure, ?
 What are the variables for this piston?
 1. temperature only
 2. temperature and volume
 3. pressure and number of molecules
 4. volume and number of molecules