Assignment2 of Liwenchao 2014.10.30
	new file:   Screenshot/Image_1_liwenchao_A2.jpg
	new file:   Screenshot/Image_2_liwenchao_A2.jpg
	new file:   Screenshot/Image_3_liwenchao_A2.jpg
	new file:   data/graph.json
	new file:   index.css
	new file:   index.html
	new file:   js/d3.js
	new file:   js/force.js