The correct example of a contact force from the options provided is:
a magnet pulling a screw toward it.
This is because contact forces involve direct physical interaction, while the other examples (a skydiver in freefall, a person standing still, and rain falling) do not involve direct physical contact forces acting on the objects in question. Keep in mind that while magnets exert a force without direct contact, they are often associated with forces that involve interaction, so strictly speaking, a magnet's action is considered a field force rather than a contact force. However, if you are looking for an example of interaction, then reconsidering this context is essential.
If we strictly adhere to the concept of contact forces, none of the answers provided illustrate a classic contact force since they depend on fields or forces that do not require physical touch. The common contact forces are those that involve direct contact, such as friction or tension.
In conclusion, if the inquiry is aimed towards purely contact forces interacting through touch, it might be worth clarifying that none of the options seem to fit. However, based on magnetic interaction, "a magnet pulling a screw toward it" is the closest response involving physical interaction, albeit not in the traditional contact sense.