Actually the return types that are defined are int,char, float or any of d basic data types. So therefore void is used when our function doesn't has to return any value. As regards parameters r concerned it has nothing to do with the return type.
You can declare d function in d following way
void fun(void,void);//same declaration
void fun(); //same as above
Which still means tat the function doesn't needs the parameters to be passed. In case you want to pass any parameter in d function which doesn't has a return type with any one of d basic data types as under:
void fun(int,int); Ans is therefore c). Okay. I hope d explanation helps u. Yeah. :)