Figure $1.$ On the left$-$hand graph, MS represents the supply of money and MD represents the demand for money; on the right$-$hand graph, AD represents aggregate demand. The usual quantities are measured along the axes of both graphe

Refer to Figure $1.$ Suppose the multiplier is $3$ and the government increases its purchases by $$25$ billion. Also, suppose the $AD$ curve would shift from $A{D}_1$ to $A{D}_2$ if there were no crowding out; the $AD$ curve actually shifts from $A{D}_1$ to $A{D}_3$ with crowding out. Finally, assume the horizontal distance between the curves $A{D}_1$ and $A{D}_3$ is $$30$ billion. The extent of crowding out, for any particular level of the price level, is

Select one:

a$.$ $$30$ billion.

b$.$ $$25$ billion.

c$.$ $$60$ billion.

d$.$ $$45$ billion.