PHP$?$a$.$One can define a function without a name. Similarly, one can define a function without a return statement.b$.$A dedicated PHP file can be created to define multiple functions but a namespace must be created for the functions in the file.c$.$If a function is defined without any parameters, it means that no arguments can be passed to the function when a function call is made.d$.$When an argument is passed by value, the original variable is sent to the function. Then any changes to the parameter in the function causes changes in the value stored in the original variable.