Ideal gas law

The above diagram shows the relationship between the pressure ( $y$ -axis) and the volume ( $x$ -axis) of an ideal gas when it changes its state in the order $A \to B \to C \to D \to A.$ The processes $A \to B$ and $C \to D$ are isobaric processes with pressures $2P$ and $P,$ respectively. The processes $B \to C$ and $D \to A$ are isothermal processes with temperatures $2T$ and $T,$ respectively. Which of the following statements is correct?

a) The volume of the gas at state $C$ is $4$ times as large as that at state $A.$
b) The volume of the gas at state $B$ is greater than that at state $D.$
c) The average speed of the molecules at state $C$ is $2$ times as large as that at state $A.$