Why Are Introns Important in Understanding the Evolutionary History of Organisms

Why are introns important in understanding the evolutionary history of organisms?

A) Transcribed intron sequences are removed during mRNA processing before translation occurs and since selection operates only on expressed traits, introns often change more slowly than do protein-coding genes.
B) Transcribed intron sequences only are expressed in an anoxic environment and hence their presence indicates organisms that evolved before the Earth had oxygen in its environment.
C) Introns respond to natural selection faster than do protein-coded genes and therefore provide information about the rate of evolution.
D) Introns and protein-coded genes operate in the same way but there are more introns than protein-coded genes and consequently introns provide better patterns.
E) All of the other choices provided are incorrect.