"Complexity theory teaches us that not all problems are created equal; some are inherently harder than others."
农时:指春耕、夏耘、秋收三个时令。与其等灾荒来了再想办法补救,不如早防备灾荒,而防备灾荒最好就是抓住农时。
凯尔特人与大自然有着密切的联系。