Question

 If a machine is lubricated with oil

(a) the mechanical advantage of the machine increases

(b) the mechanical efficiency of the machine increases

(c) both its mechanical advantage and efficiency increase

(d) its efficiency increases, but its mechanical advantage decreases

Answer 1

The correct answer is option (b) the mechanical efficiency of the machine increases 

EXplaination::
in cycle when we put oil as a lubricant on its disc the friction decreases and mechanical efficiency that  is speed increases {smoothness}