(1) negotiorum gestio. Because he took the initiative to find the owner after moving the cow home and raising it, he didn't mean to take it for himself. At the same time, helping the owner to look after the cattle belongs to the management without cause.

(2) Party A's compensation. Because cows are armor. It's A's fault that A didn't take good care of the cattle, which led to the loss of B's crops.

(3) A. Because the cow died because the cowshed collapsed due to the earthquake. The earthquake is an accident, which is beyond the control of human will and can't be foreseen by Party B. Therefore, Party B is not responsible for the death of cattle.