Two departments in a company have different numbers of employees. The average (arithmetic mean) annual salary for each department is given below.
Department X: 10 employees, mean annual salary $75,000
Department Y: 15 employees, mean annual salary $60,000

Which of the following MUST be true?
I. Every employee in Department X earns more than every employee in Department Y.
II. The median annual salary in Department X is greater than the median annual salary in Department Y.
III. There is at least one employee in Department X who earns more than at least one employee in Department Y.