title: What's the relationship of the versions of scala when I use sbt to build a scala project?
body: <p>I'm building a scala project(writen in scala 2.11) with SBT 1.x.There are a few "versions of scala" which made me puzzle.    </p>
  
  <pre><code>SBT 1.x    =&gt; scala 2.12   
  SBT plugin =&gt; scala 2.x   
  My project =&gt; scala 2.11   
  </code></pre>
  
  <p>Please help me to figure out what's the difference or relationship between them.And how SBT tells them apart when compiling or running the project?</p>