题目内容：

Watching online open classes of US top universities has become necessary for many young Chinese who find it a shortcut to make their life more meaningful, in addition to learning knowledge and language.

Guo Lei, a native of Guangzhou, has become addicted to various open courses after she watched the online video of "Justice: What's the right thing to do."The video clip was taken during an open class taught by Michael Sandel, professor of philosophy at Harvard University.

Sandel set up a situation in which a high-speed train with a technical problem is running towards five people who are working on the current track, while there is only one worker on the adjacent (相邻的) track.He inspired students to discuss what the driver should do -- to change the direction for five lives -- which apparently will kill the other -- or to do nothing and allow five people to die.

Guo said she was immediately attracted by the topic and the discussion of the Harvard students about morality and justice.She even introduced the case to her colleagues for discussion, since Sandel did not give an answer, unlike most Chinese teachers she knew before.

The inspiring and lively teaching style of American professors refreshed Guo's impression about the traditional score-oriented Chinese educational system and prompted more Chinese to frequently search and watch open class resources of American top colleges, including Massachusetts Institute of Technology (MIT) and University of California Berkeley.

On China's social networking websites, such as renren.com, kaixin001.com and sina.com, netizens have spontaneously formed many study groups to share video resources and exchange opinions.Volunteers have added English or Chinese subtitles onto the videos to help more Chinese enjoy the videos without language difficulties.

"The popularity of American open classes reflects the spir it of sharing," said Yu Xinke, Vice chancellor with the Continuous Education School of South China University of Technology.

1. If the train driver changes the current track , how many people will be killed?(No more than one word)

2.Why can Chinese have no difficulty enjoying the foreign class videos?（No more than 10 words）

3. Besides knowledge and language, list three other things Chinese can learn from watching such foreign online class? (No more than 15 words in total)

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4.What is the main idea of this passage?  (No more than 10 words)