（C）

    Jim went to school to study history, but when he finished his first year, he didn't pass the exam and the teacher said to him, “You have to leave school.”

    When the boy's father heard this news, he was much worried. He came to the school to see the teacher. He found the teacher in the office and asked the teacher to let Jim go on with his studies the next year.

    “He is a good boy. He always does well in history,” said Jim's father, “and if you let him pass the exam this time, he will do better next year and pass the exam.”

    “No, no, that's impossible!”answered the teacher, “Last month I asked him when Napoleon（拿破仑）died and he didn't know.”

    “Please sir, give him another chance.”said Jim's father,“You know we don't have any newspapers in our house, so nobody in our family knew that Mr. Napoleon was ill.”

关于电磁波，下列说法正确的有（   ）