If initially the money supply is $1 trillion, velocity is 5, the price level is 1, and real GDP is $5 trillion, an increase in the money supply to $2 trillion
选项：

A: increases real GDP to $10 trillion.
B: causes velocity to fall to 2.5.
C: increases the price level to 2.
D: increases the price level to 2 and velocity to 10.