The correct option is D focal lengths of both objective and eyepiece are decreased
Magnifying power of a compound- microscope is given by m=−lf0Dfe
where, l is length of tube
D is least distance of clear vision
f0 is focal length of objective
fe is focal length of eyepiece
So, clearly, it can be seen that focal length of objective and eyepiece needs to be decreased so that magnifying power increases.