Final answer:
A microscope, which uses two convex lenses to magnify small objects, is the correct answer. The first lens is the eyepiece and the second is the objective lens, forming a compound microscope.
Step-by-step explanation:
An optical instrument that uses two convex lenses to magnify small, close objects is known as a microscope. Microscopes are designed to enhance the details of small objects that we cannot see with the unaided eye. A compound microscope is constructed from two convex lenses, where the first lens serves as the ocular lens or eyepiece, which is close to the eye, and the second lens functions as the objective lens that captures the initial image of the specimen.
The combination of these lenses allows for significant magnification without distorting the image, unlike a simple magnifying glass which usually cannot exceed a magnification greater than 5×. The initial image formed by the objective lens becomes the object for the second lens, which then magnifies this image further, allowing the observer to view a greatly enlarged image of the object.