Employment

Question: In the context of employment law, ,which of the following statements is true?
a) Terms can only be implied into employment contracts by judges under common law
b) Employees must obey all orders given by their employer
c) employees must act with reasonable skill and care in the performance of their duties
d) Express contract terms always override implied contract terms

In the above question what does option a) mean.

Also is there any other way of implying terms into employment contracts other than by judges under common law.