The graph is falling on the left hand side and rising on the right hand side.
Since the two ends of graph are in opposite direction, the exponent of variable has to be odd. For an even exponent of leading term, the two ends are in same direction.
Since the graph is falling on left and rising on right, this indicates that the coefficient of leading term is positive.
So, the leading term must have: 1) Odd exponent 2) Positive Coefficient
