根据教授所说内容：Anyway, it’s this fossilized pollen along with the aquifers and the rock paintings, these three things are all evidence that the Sahara was once much greener than it is today. 可知石化花粉、蓄水层以及岩石画都证明撒哈拉沙漠曾经比现在有更多的植物。所以选项 A, C, E 正确。

答案: ACE