For work to be accomplished we must have (2 points) a)an action which causes movement and an opposite reaction. b)an action which causes no movement or reaction. c)a force and a movement in the opposite direction of the force. d)a force and a movement in the same direction as the force.

I think it's A, an action which causes movement and an opposite reaction

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant. 

The answer is c.  h+  and oh−  react to form water (h2o). i just took the test and i got it right. hope this !