In recent days, continuous rainfall in the southern part of the country has caused many artificial fish ponds to be flooded. Therefore, several fish-farming experts have predicted the price trends of catfish and carp? Li Qiang said: Only when the price of catfish increases, carp prices will rise; Sun Zhen said: The price of at least one of catfish and carp will rise; Wang Gang said: only if the price of carp does not rise, the price of catfish will not rise; and if the price of catfish does not rise, the price of catfish will not rise. If it turns out that all three experts' predictions are true, which of the following must be true? ['Catfish prices rise, carp prices do not rise.', 'Catfish prices do not rise, carp prices rise.', 'Both catfish and carp prices have risen.', 'Prices of both catfish and carp have not risen.']