A letter written to a 12-year-old girl in Lithuania arrived in December,almost 51 years after it was sent. Now in her 60s,Miss Klonovska said after being handed the letter,“I thought thatsomeone was playing a joke on me.” The letter included a handmade,colored rose and two paper dolls. It was sent to Klonovska by a young girl in Poland. They exchanged letters in what is known as a pen friend program when people write letters to each other without actually meeting. The letter,together with 17 others,was discovered last summer when a wall was taken down in an old post office in Vilnius. Mr. Vilutis is the owner of the building.“The workers suggested I throw the old letters away,but I called the post office instead,”Mr. Vilutis said.“I'm so happy they got interested.” The letters,from the late 1960s and early 1970s,were likely lost by a postal worker,Mr. Vilutis said. Lithuania was part of the Soviet Union then. The senders(寄件人)were family members or pen friends from places such as Australia,Poland,or Russia. Street names and their numbering have changed in Vilnius. Post office workers spent months looking for the people who were supposed to receive the letters—the recipients. Only five recipients were found. In several cases,children of dead recipients were handed a lost letter. Deimante Zebrauskaite,head of the customer experience department at Lithuania Post,said “We felt it is a moral(道义上的)duty to do this.”
 47. What can we infer from the passage?