The correct answer is (C). The two brothers should not compete with each other but work in cooperation.
(A) Fight means to engage in a physical struggle with another person. This is not what the question is asking.
(B) Conspire means to secretly plan to do something harmful or illegal. This is also not what the question is asking.
(D) Envy means to feel resentful or jealous of someone else’s possessions, qualities, or luck. This is not what the question is asking.
The two brothers should work together instead of competing with each other. This will help them to achieve their goals and build a strong relationship.