Tom and Joseph are best friends. They spent their summer vacation in Africa. When they were walking through the desert , they started to argue  about something. Tom became very angry and slapped  Joseph in the face. Joseph felt hurt, but he didn't say anything to Tom. Then Joseph wrote in the sand : "Today my best friend slapped me in the face." They kept on walking until they found a small lake. They decided to have a bath . But when Joseph got in the water, he started to sink . Tom jumped in after him and pulled him out. His friend saved his life. After he became well again, Joseph wrote on a stone : "Today my best friend saved my life." Tom couldn't understand it. "After I hurt you, you wrote in the sand. Now you write on a stone. Why?" he asked.  _ " Joseph answered. "But when someone does something good for us, we must write it on stones so that no wind can ever take it away." Tom and Joseph went on a trip in   _  .
Europe America Africa. Asia