title: How to draw straight line in d3.js (horizontally and vertically)
body: <p>I have doubts in drawing the line graph concept. Can anybody explain these coordinates?</p>
  
  <p><code>x1=5,x2=10,y1=10,y2=30</code> </p>
  
  <p>Please explain each attribute and what it represents. Also, please give me an idea about drawing a straight line vertically and also horizontally (like a cross-hair).</p>
  
  <p>I am total newbie to d3.js graphs, so please help me. Any help would be appreciated.</p>