Select an Appropriate Expression to Complete the Following Method, Which

Select an appropriate expression to complete the following method, which is designed to return the number of elements in the parameter array numbers. If a value appears more than once, it should be counted exactly once. public static int countElementsOnce(int[] numbers)
{
Set<Integer> values = new HashSet<Integer>() ;
For (int num: numbers)
{
Values.add(num) ;
}
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}

A) return numbers.length;
B) return values.length() ;
C) return values.size() ;
D) return numbers.length - values.size() ;