A7 On the track, four dogs are placed on numbered positions. In how many different ways can they be arranged?
(A) 4
(B) 8
(C) 16
(D) 24
(E) 48
A7. The first dog, when choosing a seat, can choose from four seats, the second from three, the third from two, and the last from one empty seat. Considering the product rule $4 \cdot 3 \cdot 2 \cdot 1=24$.