What are the most common biological specimens found at crime scenes?

The selection of blood, semen, and saliva as the most common biological specimens found at crime scenes is accurate due to their prevalence in forensic investigations. Blood is a crucial specimen because it can provide a wealth of information, including DNA profiles and blood type, which can help identify individuals present at the scene or the victim's identity. Semen is typically associated with sexual assaults and can also yield DNA evidence crucial for linking a suspect to a crime. Saliva can be found in various contexts, such as in bite mark analysis or from various interactions with items at a crime scene, and it too can furnish DNA evidence.

These biological fluids are valuable because they not only provide identification data but also can indicate whether a crime has occurred or the circumstances surrounding it. The significance of these specimens is underscored by their reliability and the advances in forensic science that allow for accurate analysis and matching, making them commonly sought after in crime scene investigations.

In contrast, the other combinations of specimens, while potentially useful in certain contexts, do not offer the same level of identification and evidence-gathering potential as blood, semen, and saliva do in the majority of crime scene scenarios.