There is a cyclic process abcda carried out in a gas. Which of the following statements is correct?
A、The work done in the process is equal to the area under ab minus the area under dc.
B、The work done in the process is equal to the area enclosed by the cyclic process.
C、The work done in the process is equal under the curve abc.
D、The work done in the process is equal to the area under the curve adc.