Which is not a way to accelerate an object?
a. speed it up
c. change its direction
b. slow it down
d. apply balanced forces

Slowing an object down is not a means of accelerating it. It actually decelerates the motion of an object. Speeding it up, changing its direction and applying balanced forces accelerate an object. In order for an object to accelerate, a force must be applied. It follows Newton’s second law of motion where it states that a body at rest remains at rest unless a force is acted upon it. When you move an object, you are exerting a force onto it. By exerting a force on the object, you are actually displacing it from its initial position. You cannot apply force to the object without altering its position. Keep in mind that when you exert work, you are exerting energy too. 

Efficiency is an action of doing something. for example when you take a test. good efficiency means you did well but bad effeciency or no effiency means you did bad.