Question 80
It is given that there are two sets of real numbers $A = \{a_1, a_2, \dots, a_{100}\}$ and $B = \{b_1, b_2, \dots, b_{50}\}$. If there is a mapping $f$ from $A$ to $B$ such that every element in $B$ has an inverse image and
$$
f(a_1) \le f(a_2) \le \dots \le f(a_{100}),
$$
then the number of such mappings is ( ).
(A) $C_{100}^{50}$ (B) $C_{50}^{50}$ (C) $C_{100}^{49}$ (D) $C_{50}^{49}$
$$
f(a_1) \le f(a_2) \le \dots \le f(a_{100}),
$$
then the number of such mappings is ( ).
(A) $C_{100}^{50}$ (B) $C_{50}^{50}$ (C) $C_{100}^{49}$ (D) $C_{50}^{49}$