In a Phylogenetic Tree of Primates, a Gene Involved in the Production

Multiple Choice

In a phylogenetic tree of primates, a gene involved in the production of brain peptides shows 25 silent substitutions but only 4 missense substitutions.From these results, we can infer that

A) the gene is a pseudogene.
B) strong purifying selection has been operating on the gene.
C) strong positive selection has been operating on the gene.
D) the evolution of the gene is affected only by mutation and genetic drift.
E) the gene is following a molecular clock.