Question

why twin brothers quarrel
what plants need to flourish
how important crops originated

Explanation:

The first question about why twin - brothers quarrel can be related to psychology as it involves human behavior and relationships. The second question about what plants need to flourish is related to biology as it pertains to the study of plant life. The third question about how important crops originated is also related to biology as it concerns the origin and development of plant species used as crops.

Answer:

Psychology for the first question, Biology for the second and third questions.