Employment

Question: An employee has been informed by their employer that they are legally obliged to obey any lawful and reasonable orders.
Which of the following statements is true?
a) This is an example of a contractual term implied by common law
b) This is an example of a contractual term implied by statute
c) This is most likely to be an express contract term
d) The employer is incorrect,, there is no legal obligation for an employee to obey lawful and reasonable orders
In the above question. I thought the correct option is c) since the employer has specifically told the employee. So why is this option not correct and why the correct option is really the correct one.