One mole of a diatomic ideal gas undergoes a cyclic process ABC as shown in figure. The process BC is adiabatic. The temperature at A,B and C are 400K, 800K and 600K respectively. Choose the correct statement:
A. The change in internal energy in the process AB is `-350R`.
B. The change in internal energy in the process BC is `-500R`
C. The change in internal energy in whole cyclic process is `250R`.
D. The change in internal energy in the process CA is `700R`.