There are sources of protein, and this may not surprise you are multiple, and they come in these various sources. These are all good sources of protein but not the only ones.

如你所知,依次为,鱼类和海鲜,家禽,肉类乳品,鸡蛋,豆类,酱油

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选