What happens to the trait when proteins connect in different ways?

I think it changes the physical appearance of that certain trait. For example, eye color. If the proteins are set up a certain way for brown eyes, then changed, there would be blue eyes.

The correct answer for this question is:
A farmer planted legumes and cabbage in the same field that is devoid of fertilizers. The yield from this field is better than the cabbage planted inanother field without legumes. The reason for this is because (A) nitrogen-fixing present in the roots of legumes aid enrichment of nitrogen in the soil.