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    One day an ant was drinking at a small stream and fell in. She made desperate efforts to reach the side, but made no progress at all. The poor ant almost exhausted was still bravely doing her best when a dove saw her. Moved with pity, the bird threw her a blade of grass, which supported her like a raft, and thus the ant reached the bank again. While she was resting and drying herself in the grass, she heard a man come near. He was walking along barefooted with a gun in his hand. As soon as he saw the dove, he wished to kill it. He would certainly have done so, but the ant bit him in the foot just as he raised his gun to fire. He stopped to see what had bit him, and the dove immediately flew away. It was an animal much weaker and smaller than herself that had saved her life.

下列行为中，属于有利于同学之间相互促进、共同进步的是（）