Evolutionary tracing has identified clusters of the most invariant amino acids in the SH2 domain family. Which of the following is true regarding these sites?

A) Mutation in these sites generally keeps the protein functional.
B) The invariant amino acids generally have negatively charged side chains.
C) These sites correspond to the binding site for peptides containing phosphorylated tyrosine.
D) The amino acids at these sites are generally hydrophobic.
E) These sites have evolved fast because they have critical functions.