Define a recursive function `fact(n)` which takes as input a nonnegative integer ( n ) and outputs ( n! ), the factorial of ( n ).

a) ( n! = n × (n-1)! )
b) ( n! = n × fact(n-1) )
c) ( n! = fact(n-1) × fact(n) )
d) ( n! = n × (n+1)! )