Which situation would require the operator to be overloaded as a non$-$member $($i$.$e$.$ outside class$)$ function?

a$.$ All operators can be overloaded both as member $($i$.$e$.$ inside class$)$ and non$-$member function.

b$.$ The left most operand $($or parameter$)$ is a class object $($or a reference to andass object$).$

c$.$ The left most operand $($or parameter$)$ is an integer.

d$.$ The operator returns a reference.