You could increase the mechanical efficiency of this screw by

You can increase mechanical advantage by making the drive lever longer, yet it wouldn't help the efficiency. The only way to increase the mechanical efficiency of the screw is to decrease the friction - by lubrication, changing the material, or thread design.
Thus, the best answer would be letter b.reducing friction along the screw threads 
Here are the choices:
A making the screw threads longer
B. reducing friction along the screw threads
C. making the inclined plane longer
D. adding more threads to the screw

That would be a working theory.