Correct answer is B. A real object has a positive object distance.


The lens equation is an important topic in physics and optics because it allows quantifying the relationship between an object and an image. There are three key concepts involved in a lens equation: object distance, image distance, and focal length (see Figure 1).

The lens equation scheme.
Figure 1. The lens equation (Source: http://hyperphysics.phy-astr.gsu.edu)

The object distance is the space between the object and the point of incidence where the rays fall on the lens.

The image distance is the space between the lens and the image.

The focal length is defined by the distance from the center of a lens and its focal point.

With a real object, the object distance will be positive because it is located in front of a lens. Image distance can be both positive (if an image is real) and negative (if an image is virtual).