The figure shows the population change curve of lynx and mountain rabbit in Canadian forests in North America during the 90 years from 1845 to 1935. Answer related questions according to the picture: (1 (1) As can be seen from the figure, A increases and B increases; The increase of B leads to the decrease of A, and the decrease of A leads to the decrease of B. Therefore, it is concluded that the change of the amount of B is similar to that of A, but there is a lag. This shows that there is a predatory relationship between them. The predator is B and the prey is A, so the energy flows from the predator to the prey, that is to say, the energy flows from A to B. Therefore, the population change of the mountain rabbit is represented by the letter A, and the year with the largest number reaches 10.

(2) The food chain in this food web is grass → mountain rabbit → lynx. If the number of mountain rabbits can increase sharply in a period of time, the biological factor is mainly the increase of edible plants; (2) The dramatic decrease of lynx;

(3) Lynx lives in forest bushes, dense forests and rocks, and belongs to forest ecosystem. Lynx preys on a certain number of mountain rabbits, so that the forest vegetation is not excessively destroyed, thus maintaining the stability of the system.

(4) During the study period of 1890 ~ 1935, the K value of the mountain rabbit in this ecosystem was about 60000. From any moment in the figure, when the mountain rabbit population reaches the K value, the K value of the lynx population changes later than that of the mountain rabbit.

So the answer is: (1) one 140+040K or 140000.

(2) The number of edible plants increased and the number of lynx decreased sharply.

(3) Lynx preys on a certain number of mountain rabbits, which will not destroy the forest vegetation excessively, thus maintaining the stability of the system.

(4) 60,000 is later than.