Which of the following scenarios would allow you to study the relationship between pressure and temperature of a gas according to the combined gas law without volume changing?
a. a balloon of gas heated with a hair dryer
b. a closed thermos of air warmed a little in an oven
c. filing a 2 liter bottle half full of water then closing it and squeezing it
d. Heating a thermos of air but allowing air to leak out to keep the pressure low.