相关Whatmustyou的文学知识

问题详情：完形填空Whatmustyou 1 whenyoureceiveapresentforyourbirthday?Youhavetositdownandwriteathank-youletter.Thewords“Thankyou”areveryimportant.Wehavetousethemoften.We 2 whensomeonegivesusadrink...