text: 'use strict';
  
  /* declare and assign variables as described in the comments
  
    pay close attention to how each variable is used!
    - is a variable assigned a value when it is declared?
    - is a variable reassigned later in the script?
  
    your challenge is to decide whether to use let or to use const
    - use let if
      the variable is declared without an assignment
      or the variable is ever reassigned later in the script
    - use const if
      the variable is declared with a value and never reassigned
  
  */
  
  
  let x = 'a';
  console.log(x); // should print 'a'
  
  let y = 'b';
  console.log(y); // should print 'b'
  
  console.log(x); // should print 'a'
  
  let z;
  console.log(z); // should print undefined
  
  console.log(y); // should print 'b'
  
  z = 'c';
  console.log(z); // should print 'c'
  
  y=y+'d';
  console.log(y); // should print 'bd'
  
  console.log(x); // should print 'a'
  