Answer:
a is the answer
Step-by-step explanation:
A telescope uses a curved lens or mirror (called an objective) to collect light from distant objects and to focus that light to an image. The bigger objective lens or mirror collects a lot of light and creates brighter and sharper images. The focused image formed by the objective lens of a telescope is magnified by a smaller second lens called an eyepiece. As visual observers, we look into the eyepiece to see the bright magnified image from the objective. But an eyepiece used with a small lens or mirror simply magnifies a dim and fuzzy image. The detail and brightness of an image all comes down to the amount of light collected by the objective lens or mirror. And that depends on its diameter of the objective, also called the aperture.
look at the picture