2. There are many different opinions about "five grains" in ancient times, mainly including two kinds: one refers to rice, millet, millet, wheat and glutinous rice; The other refers to hemp, millet, millet, wheat and glutinous rice. The difference between the two is that the former has rice without hemp, while the latter has hemp without rice. The ancient economic and cultural center was in the Yellow River valley, and the main rice producing area was in the south, while the rice planting in the north was limited, so there was no rice in the original "five grains".