ETS Practice Test: GR0177 (First problem involves a pendulum)

Problem 6: An ideal monatamic gas expands quasi-statically to twice its volume. If the process is isothermal, work done by the gas is Wi. If adiabatic, work done is Wa. Which is true?

(list of options, the correct answer being E)

E) 0 < Wa < Wi

Can someone explain to me why isothermal work is necessarily larger than adiabatic work?