Question

look at the statements about the 1930s.
loss of grasses left topsoil loose and unprotected.
high winds frequently blew on the great plains.
valuable topsoil needed by farmers was thus blown away.
which statement belongs on the blank line?
millions of acres of productive farmland became barren desert.
ranchers allowed their herds to overgraze and damage grasses.
farmers did not rotate crops, and soil nutrients were used up.

Explanation:

The first three statements describe a cause - effect chain: loss of grasses → loose topsoil → high winds blow topsoil away. The next logical step in this chain is the consequence of the topsoil being blown away. When topsoil (which is crucial for farming) is blown away, the land becomes less productive. The statement "Millions of acres of productive farmland became barren desert" is the result of the previous events (loss of topsoil due to wind erosion). The other two options ("Ranchers allowed their herds to overgraze and damage grasses" and "Farmers did not rotate crops, and soil nutrients were used up") are causes (like the first statement "Loss of grasses...") rather than the final effect in this particular chain.

Answer:

Millions of acres of productive farmland became barren desert.