The most important property of any microscope is its resolution (D) and can be calculated from the formula

\(D=\frac{0.61 λ}{N \sin α}\)

where D is minimum distance between two distinguishable objects, λ is the wave length of incident light, α is the angular aperture and N is the refractive index of the medium. Given below are several suggestions to improve the resolution of a microscope:

A. decrease the wave length of incident light

B. increase the wave length of incident light

C. use oil which has a higher refractive index

D. use oil because of its lower refractive index

Which one is the correct suggestion?