The following factors were necessary preconditions for the cotton boom of the $1830$s except:

a$)$ the general expulsion of Native Americans from the U$.$S$.$ South.

b$)$ new varieties of cotton better suited to the southern climate and soil.

c$)$ inexpensive barbwire fencing that allowed planters to mark off their land.

d$)$ inexpensive farmland with investors on both sides of the Atlantic ready to fund plantations.