The correct answer is option 4: two convex lenses of unequal focal lengths.

A refracting telescope is a type of optical telescope that uses lenses to gather and focus light to create an image. It consists of two main components: the objective lens and the eyepiece.

The objective lens is responsible for gathering light and forming the primary image. In a refracting telescope, this lens is a convex lens. It can be made up of two lenses, where one lens has a shorter focal length than the other. This arrangement helps to correct for chromatic aberration, which is an optical effect that causes different colors to focus at different points.

The eyepiece, on the other hand, is responsible for magnifying the primary image formed by the objective lens. In a refracting telescope, the eyepiece is also a convex lens. However, in this case, the focal length of the eyepiece does not need to be unequal.

So, in summary, a refracting telescope consists of two convex lenses, with unequal focal lengths, to gather and focus light, and then magnify the resulting image.