Students are very interested in computers, the Internet and mobile phones. Using new technologies in the classroom can be very helpful for them.

    Mobile phones can be very useful in the classroom. When students speak or act, teachers can use them to record students, take photos and show them to students. Using mobile phones in class is a fun way of doing some interesting language work.

    How to use the Internet and mobile phones in class? Please remember the following key points (要点) :

    Use the Internet with your students in many different ways, if possible.

    Try to find good websites for your students.

    Use your mobile phone in class to record your students, take photos and play recordings.

    Ask your students to listen for the pronunciation mistakes when you play the recordings back to them.

阅读材料，回答问题。

时代呼唤“绝对忠诚”。湖南卫视新闻团队从今年4月起，以“绝对忠诚”为题，陆续推出一批当代科学家的感人事迹，展示他们坚守信念、忠于祖国、乐于奉献、勇攀高峰的可贵精神。节目播出后，引发社会各界广泛共鸣，被媒体誉为“弘扬主旋律、传播正能量的新闻宣传精品力作”。有网友留言：一个个鲜明的军工科学家，用“绝对忠诚”置顶了时代正气歌，那种直达心灵的冲击与快感让人们久久不能平静……

为做好《绝对忠诚》系列报道，创作团队与主人公同吃同住同劳动，通过“零距离采访”和“隐藏式拍摄”，记录了大量鲜为人知的细节和催人泪下的故事，并通过镜头拍摄和音乐、画面的精心选择，增强了作品的艺术感染力。该栏目还第一时间将节目视频在各大主流网站同步推出，吸引了广大网民积极参与，有效扩大了传播效果。

设集合A={1，2，3}，B={4，5}，C={x|x=b﹣a，a∈A，b∈B}，则C中元素的个数是（　　）