人类的第一个朋友是狗，它忠诚陪伴，带来无尽欢笑与温暖。4399小游戏免费马上玩

　　He has shared our lives for 20,000 years. Along the way, he has helped us find food, kept our livestock, protected us from our enemies, guided us in extreme conditions, and saved us from peril. Now, he comforts us, relieving loneliness and helping us cope with old age. How did dogs come about?