What are latent prints caused by at a crime scene?

Latent prints are primarily caused by small amounts of oil or grease that are naturally present on the skin of our fingers. When a person touches a surface, these oils can leave an impression that is often invisible to the naked eye, hence the term "latent." These prints can be effectively processed and revealed using various techniques and chemicals, making them vital pieces of evidence in crime scene investigations.

High pressure, water condensation, and friction can contribute to the formation of other types of evidence or marks but do not directly explain how latent prints are created. High pressure may cause visible changes or damage to surfaces, while water condensation can lead to the formation of temporary moisture marks. Friction on surfaces may create wear or other forms of evidence, but the specific mechanism that leads to the formation of latent fingerprints is the transfer of oils or greases from the skin onto a surface, making option B the best answer.