There is a lion in a forest. Every day he goes about to look for food. The small animals in the forest are all afraid of him. Not far from the forest there are four bulls(   ). They are good friends, and often go about together. The lion tries many times to catch them, but can't do so. Every time he comes near, the four bulls stand together to fight him. So he can do nothing to him. One day the bulls have a quarrel(   ). After that each of them goes his own way. When the lion sees this, he is happy. He catches one bull and eats him up. Then he catches another. One by one he catches all the four bulls and eats them up. Why can't the lion want catch the bulls at first?
Because the bulls are too big. Because the bulls are good friends. Because the bulls stand together to find him. Because he is not strong enough to fight bulls.