:4. Solution.  The first statement is true since the population
histogram follows the normal curve.

      The second statement is false since the SE of the
population incomes is $5,000, not $500.

: the chance that X is between
$19,000 and $21,000 is either 0% or 100%.

     The fourth statement is true since the SE of the sample
average is $5.000/10 = $500.

      The correct answer is "two".