A gas confined in a cylinder compressed by an external force performing 1000 joules of work on a piston. How much work should be supplied to keep the thermal energy (or temperature) constant? Note: + indicates heat is added, - indicates heat is removed.
(a) 0 joules
(b) 2000 joules
(c) -1000 joules
(d) +1000 joules
(e) -2000 joules