What is the problem associated with historical DNA samples?

A. They are less in amount thus amplification is difficult

B. Because the samples are very old, there can be contamination

C. They degrade during repeated cooling and heating cycles

D. As the samples are old, the standard sequences for comparison is not present

Explanation: The historical DNA samples though can be analysed but the main problem with them is that the duration for which they can be used. As the samples are very old they are often contaminated by bacteria.