title: How to draw line X=1?
body: <p>I know how to draw a line with scatter plot options where X is the independent and Y the dependent variable.  </p>
  
  <p>In the scatter plot of that data I need to add another line: X=2. I have the following data:</p>
  
  <p><img src="https://i.stack.imgur.com/zdRYO.jpg" alt="enter image description here"></p>
  
  <p>But how to draw a line X=1 ? </p>