19. (14 points) The express train from Yueyang to Pengzhou includes the starting station and the terminal station, a total of six stations, which are denoted as $A, B, C, D, E, F$. One day, Zhang Bing and 18 other passengers boarded the same carriage from Yueyang. Among these passengers, some were from Hubei, and others were from Hunan. Zhang Bing, who knew all the passengers in the carriage, observed that: except for the terminal station, at each station when the train arrived, the number of Hunanese in the carriage was the same as the number of passengers who got off, and no new passengers entered this carriage during the journey. Zhang Bing further observed that: when the train left station $B$, there were 12 passengers in the carriage; when the train left station $D$, there were still 7 passengers in the carriage; when he was about to get off at station $F$, there were still 5 passengers in the carriage. How many Hubei people and Hunanese were there in this carriage at the beginning? And how did these numbers change during the journey?
19. From the conditions, 7 people get off at station $B$, meaning 7 of the 19 passengers are from Hunan. At station $E$, 2 people get off, meaning there are 2 Hunan people on the route $D-E$. There are at least 2 Hunan people on the route $C-D$, and at least 2 people get off at station $D$. Therefore, there are at least 9 people on the train after station $C$. Also, since $\frac{12-7}{2}>2$, there are at least 3 Hunan people on the route $B-C$. Thus, there are at most 9 people on the train after station $C$, so there are 9 people on the train after station $C$.
In summary, there are 7 Hunan people and 12 Hubei people on the $A B$ segment; 4 Hunan people and 3 Hubei people get off at station $B$, 2 Hubei people get off at station $D$, and 2 people get off at station $E$.
(Liu Jinguo provided) 1 Hunan person gets off at station $C$.