The definition of Ethical Hacking states

a$.$ Hacking is legal if it is done to find a weakness in a computer or network system for a colleague

b$.$ Hacking is legal if it is done to find a weakness in a computer or network system for testing purposes

c$.$ Hacking is legal if it is done to find a weakness in a computer or network system for personal use

d$.$ Hacking is legal if it is done to find a weakness in a computer or network system for a client

e$.$ Not listed