【作者(必填)】Chen

【文题(必填)】

【年份(必填)】2011

【全文链接或数据库名称(选填)】https://www.amazon.com/Twenty-Problem-Solving-Mathcounts-Competitions/dp/1453784969/ref=pd_bxgy_14_img_2?_encoding=UTF8&pd_rd_i=1453784969&pd_rd_r=b3cffc07-af40-11e8-9f1d-0fdf2b561195&pd_rd_w=wAIRG&pd_rd_wg=6oMQU&pf_rd_i=desktop-dp-sims&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=6725dbd6-9917-451d-beba-16af7874e407&pf_rd_r=YR7TF36WYZQ7KNNKDYT8&pf_rd_s=desktop-dp-sims&pf_rd_t=40701&psc=1&refRID=YR7TF36WYZQ7KNNKDYT8