味觉的形成：____接受刺激，产生神经冲动，神经冲动通过神经传到大脑皮层，在大脑皮层形成____、____、____、____四种基本味觉．

    People in the West didn't know coffee or tea two hundred years ago. They were 1 to drink them because they thought coffee or tea could kill a person. Once the king of England decided to find out 2 it was true.

    There were two brothers in prison(监狱) at that time.They would be killed 3 a few days because they did wrong. The king said, "I shall let them live but they must drink coffee or tea to the end of their lives. One brother must drink coffee and 4 must drink tea every day." And they followed the king's words.

    They both lived many years. At last, the elder brother died when he was eighty-three years old.The younger one died a few years later. After that, people 5 that coffee and tea were not bad to man.

《使至塞上》尾联用典故流露了向往建功立业的心情。这个典故隐含在____两个字中。