Humans' main source of food during the early Paleolithic Era was a from the sea. b from hunting and gathering. c from farming and growing crops. d from raising livestock and cattle.

B. from hunting and gathering is the correct answer. The Paleolithic Era was a prehistoric period in human history. Humans had only developed primitive tools. They had not yet discovered how to farm and raise livestock, and the few who lived near water still preferred to hunt and gather.