ANS:E - all the above.

Let's go through each statement to confirm:

1. Spherical aberration may be reduced by diminishing the aperture - This is correct. Diminishing the aperture can help reduce spherical aberration by limiting the range of incident light rays.
2. Spherical aberration may be minimized by replacing the single lens with a combination of lenses - This is also correct. Using a combination of lenses can help correct spherical aberration by compensating for the errors introduced by each individual lens.
3. In telescope objectives, a combination of convex lens and concave lens is used - This statement is true. Telescope objectives often use a combination of lenses, including convex and concave lenses, to minimize aberrations and improve image quality.
4. In eyepieces, two plano-convex lenses placed at a certain distance apart are used - This statement is also accurate. Eyepieces commonly utilize two plano-convex lenses arranged at a specific distance to magnify and focus the image formed by the telescope objective.