hints:

序號不用寫~

標(biāo)點符號不用寫~
be an essential ingredient of sharpen one's intellect achieve and maintain something
be an essential ingredient of 是...的必備條件 sharpen one's intellect 提高某人分析問題的能力 achieve and maintain something 實現(xiàn)并且保持某種狀態(tài)