Without any additional circuitry, an 8:1 MUX can be used to obtain:

(1) Some but not all Boolean functions of 3 variables (2) All function of 3 variables but none of 4 variables (3) All functions of 3 variables and some but not all of 4 variables (4) All functions of 4 variables

(1) Some but not all Boolean functions of 3 variables (2) All function of 3 variables but none of 4 variables (3) All functions of 3 variables and some but not all of 4 variables (4) All functions of 4 variables