Final answer:
The corn become a signature food crop in southwestern cultures in a. Prehistoric times.
Step-by-step explanation:
The cultivation of maize, also known as corn, became a signature food crop in southwestern cultures in Prehistoric times. The earliest evidence of maize cultivation in the region dates back to about 2250 BCE. Over time, groups in the Southwest, such as those in northwestern New Mexico and near Tucson, Arizona, developed sophisticated irrigation systems and built settlements around maize cultivation.
Maize agriculture eventually led to the rise of settled agricultural communities in the Southwest and Eastern Woodlands. So therefore maize became a signature food crop in southwestern cultures in prehistoric times, with evidence of cultivation dating back to around 2250 BCE. Settlements and irrigation systems were developed around maize cultivation, leading to the rise of agricultural communities. The correct answer is a. Prehistoric times.