It is d
Explanation: 40/30=0.75 because there are 40 flowers in total and only 30 are red so the % of there being red flowers is 75% or 0.75 (same thing)
DNA/fingerprints are all unique, therefor it is easy to match a fingerprint to a person thus they use this mechanism in criminal investigations because only one person woul have matching DNA to the prints on the scene, and that is the criminal.
Hope this helps :)