Explanation: Sources have also made unsolicited ". ① a basis for a source. ② means a foundation. Source: Song Lu, "read Mr. Wan Ling poem" exhaustive exercise power sources are unsolicited. " Examples: Chinese characters than some of her friends Fengmei Qing Gao. Meridian of the exchange securities market, that she is '~'. ★ Mao Dun "Midnight" Eleventh