C

The focal lengths of the objective and the eyepiece are crucial for determining various properties of the telescope.
(i) Intensity of the image: The intensity is related to the radius of curvature (R) of the lenses, as the larger the radius, the greater the intensity. Hence this corresponds to option [A].
(ii) Angular Magnification of the lens: The angular magnification depends on the focal lengths of the lenses, but does not relate to dispersion, which pertains to how light spreads out in different wavelengths. Therefore, this matches with option [B].
(iii) Length of telescope: The length of the telescope is determined by the sum of the focal lengths of the objective (fO) and the eyepiece (fe). Therefore, this statement correctly relates to option [C].
(iv) Sharpness of image: Sharpness and clarity of the image are altered by spherical aberration, which occurs due to the shapes of the lens. Thus, this corresponds to option [D].
Therefore, the answer for length of telescope which directly relates to focal lengths is option [C], leading to the conclusion: Length of telescope relates to Focal length fO & Fe.