When an ideal gas in a cylinder was compressed isothermally by a piston, the work done on the gas was found to be $1.5\times {10}^4\mathrm{joules}$. During this process about

• A

  $3.6\times {10}^3$cal of heat flowed out from the gas

• B

  $3.6\times {10}^3$cal of heat flowed into the gas

• C

  $1.5\times {10}^4$cal of heat flowed into the gas

• D

  $1.5\times {10}^4$cal of heat flowed out from the gas