C i think is the answer cause he did all the others except for answer c.
The 'global warming' would have been a cause that led to the agricultural revolution. As climates became warmer, crops would have grown more sufficiently and domesticated animals would have had a higher chance to survive which increased food supplies and also led to the rise of the industrial revolution.
<span>Earlier to the 1800s, settlers had
to cross the United States by means of horses and wagons. By the early 1800s,
canals began to assist opening up the interior. In the late 1800s, the
railroads facilitated people settle down to earlier unreachable areas in the
west. By the 1900s, the U.S. federal highway system assisted people effortlessly
migrate through the country. </span>
