Fingerprints are useful in crime detection because

Step 1: Analyze the question The question asks why fingerprints are useful in crime detection. We need the reason that makes fingerprints reliable for identifying a specific person.

Step 2: Explain the concept Fingerprints are patterns of ridges (loops, whorls, and arches) on the skin of the fingertips. These patterns form before birth and stay the same throughout life. They are unique to each individual, even identical twins have different fingerprints. This is why they can be used to link a particular person to a crime scene.

Step 3: Evaluate each option

• A. The police have sophisticated fingerprint machines: This is about equipment, not about why fingerprints themselves are useful. Even with the best machines, prints would be useless if they were not distinctive.
• B. Thieves may leave their prints at the scene of a crime: This is true and explains how prints are found, but it does not explain why they can identify a person. Without uniqueness, a print left at the scene would prove nothing.
• C. No two people have the same fingerprint: This is the fundamental biological reason. Because each person's print is unique, a match points to one individual only.
• D. Fingerprints are easy to make: This is irrelevant to crime detection.

Step 4: Answer

Tip: In exam questions on identification (fingerprints, DNA), look for the keyword "unique" or "no two people the same". Uniqueness is the scientific basis, while other options usually describe circumstances or tools.