根据短文理解, 从A、B、C、D四个选项中选择最佳答案填空。

    My friend John is a student. Last year, he went to Japan and stayed there  1two months. I was2 that John was able to 3such a long holiday in Japan because he was 4  . "How did you get so  5  money, John?" I asked. "I thought you could stay in Japan for 6  two weeks." "It was easy," he answered. "I got a job in Japan." "A job? What did you do?" "I gave English lessons  7  a shop owner, and we became good friends." "But you are8  teacher!" "Mr Tanaka, the shop owner, knew l was not a teacher, but he said he had a lot of American customers, so he wanted to learn English. I spent three hours a day 9  to him. In return, he gave me a room, three meals a day and some money."

    "Did he learn 10 English?'' "I don't know," John said, "but I learnt a lot of Japanese."