作者在《出师表》中所表达的思想可用“_________”“_________”六个字来概括；“____________”一句，高度概括了先帝创业过程中的艰难险阻，也表达了作者愿与先帝患难与共的深情。

Which of the following, if true, gives the best explanation for the growing disparity in the earning levels of the two groups in the graph presented above