A .When the resultant force on an object is zero, it will remain at rest if it is at rest, or continue to move in a straight line at a constant velocity if it is in motion. So , the answer will be a net force greater than zero .
B . An unbalanced force (net force) acting on an object changes its speed and/or direction of motion. An unbalanced force is an unopposed force that causes a change in motion. A net force = unbalanced force. So , the answer will be unbalanced forces .
The answer is descent with modification. Descent with modification practically means that a species have changed appearance wise over long periods of time to adapt to their environments better.
