The Comparison of Two Bullets Is Possible with the Comparison

The comparison of two bullets is possible with the comparison microscope. Such a study is made difficult by the fact that:

A) the presence of grit and rust can to some degree alter the marking on bullets fired through the same barrel.
B) evidence bullets often are distorted on impact and only small areas are found with intact markings.
C) lands and grooves are subject to wear and tear and hence striation markings are susceptible to continuing change.
D) all of the above
E) none of the above