Among the Types of Questionable Forensic Evidence That Has Been

Among the types of questionable forensic evidence that has been used in courts for decades, the text mentions the chemical composition of the bullets and handwriting analysis. What is the reason these are not valid techniques?

A) Each case is unique and cannot be compared to others.
B) The error rate is too high to make the techniques useful.
C) It is very rare to find bullets and handwritten notes at the crime scene.
D) The techniques are too expensive and there are very few experts in these.