The answer is A, friction.
Friction is the force that resists movement, and that's why oil is used as a lubricant and why ball bearings are used for machines that need to move with very little friction(i.e. bike wheels, roller skates, fidget spinners)
Answer B is too vague
C will probably reduce efficiency greatly, but not specifically in a way that turns work into thermal energy.
D is the same as C, except that it places the blame on the person using the machine, not the machine itself.
Hope I helped clear it up for you :)
Answer:
The best example of hypothesis which leads to new experiment methods was done by Morgan where he used fruit flies.
1.) similar fossils were found on different continents.
2.)the continents seemed to fit together; they were like a spread apart puzzle.
3.)geographical features and mountain ranges lined up with the same rock composition
4.)glacier grooves in rocks led him to trace them out to where they started
:)
c proteins .. most used cuz it provides energy and builds muscle
