People made snowmen and had snow fights using the (a)   of popcorn.

On one (a)   hot day, the temperature rose above 110 degrees!

Corn is a plant species that is native to North America. First (a)   thousands of years ago by the early inhabitants of what is now Mexico.

Before the (a)   of early civilizations, early humans hunted and gathered food.

As people learned to grow crops for (a)   , their relationship to these organisms changed.

Over the past century, corn has also been processed in ethanol. It is burned to (a)   heat energy.

The large-scale farming and manufacturing practices of ethanol production are (a)   freshwater resources in the Midwest and severely polluting the soil, water, and air.