title: d3.js How to draw a directed graph with one node start and one node end
body: <p>Anyone knows d3.js? I have a question:</p>
  
  <p><em>Is it possible that I draw a directed graph?</em> </p>
  
  <p>Note that：the graph starts at one node and may ends with one node.So it's not a tree.</p>
  
  <p>Example:
    A->B->C,A->D->C. those are paths in one graph.</p>