As yet a challenge to explain the cause-and-effect relationship between sleep and nutrition, there may be a third factor that impacts both of them.
要解释睡眠和营养之间的因果关系，还有一个挑战，那就是可能有第三个因素对它们两者都有影响。
2
The third type of symbiosis, mutualism, benefits both partners in the relationship.
第三种共生关系是互利共生，这种关系中的双方均能受益。
3
It's as yet a challenge to explain the cause-and-effect relationship between sleep and nutrition. There may be a third factor that impacts both of them.