Which of the following types of mutations could lead to a loss of function for a protein?

a. Silent mutation within the 45th codon of the coding region

b. Point mutation in the promoter region of the protein’s gene

c. Nonsense mutation occurring at the 20th codon for the protein

d. Missense mutation in the coding region for a gene

e. Insertion of a single nucleotide in the region corresponding to the untranslated 5’ region of the mRNA