GWD-9-Q40一道逻辑题~~！！有一句话没办法理解~~

carvinhuang

Agricultural societies cannot exist without staple crops. Several food plants, such as kola and okra, are known to have been domesticated in western Africa, but they are all supplemental, not staple, foods. All the recorded staple crops grown in western Africa were introduced from elsewhere, beginning, at some unknown date, with rice and yams. Therefore, discovering when rice and yams were introduced into western Africawould establish the earliest date at which agricultural societiescould have arisen there.

我特别搞不懂蓝色highlight部分什么意思，特别是红色部分，根本理解不了，哪位能帮我翻译翻译呢？

sdcar2010

Agricultural societies cannot exist without staple crops. So agricultural societies require staple crops.
Rice and yams were staple crops introduced into western Africa.
Therefore, knowing the date when rice and yams were introduced into western Aftrica would help set the date on which agricultural societies begin in western Africa.

carvinhuang

喔！！完全明白了！！！ 漏了Agricultural societies  谢谢~！