What is the rule for the sequence 1,1,2,6,24?

_{
}(A) a_{0}=1, a_{n}=n×a_{n-1}

_{
}(B) a_{0}=1, a_{n}=2×a_(n-2)

_{
}(C) a_{1}=1, a_{n}=1/2×a_{n-1}

_{
}(D) a_{1}=1, a_{n}=n×a_(n-2)