The correct answer is: D. Length and size of the lens
A telescope is an optical instrument that aids in viewing distant objects by collecting light and magnifying it. A microscope is an optical instrument that aids in viewing very small objects by collecting light and magnifying it.
Telescopes are typically much larger than microscopes. This is because they need to collect more light in order to see distant objects. Microscopes, on the other hand, only need to collect a small amount of light in order to see very small objects.
The lenses in a telescope are also larger than the lenses in a microscope. This is because they need to be able to collect more light. The lenses in a microscope, on the other hand, only need to be able to collect a small amount of light.
Therefore, the correct answer is: D. Length and size of the lens.