Base substitution mutations can have the following molecular consequence except
Option 'a' is silent mutation, option 'b' is missense mutation, and option 'd' is nonsense mutation. All three are types of point mutation (base substitution mutation). Option 'c' is frame-shift mutation.
Changes one codon for an amino acid into another codon for that same amino acid
Codon for one amino acid is changed into a codon of another amino acid
Reading frame changes downstream to the mutant site
Codon for one amino acid is changed into a translation termination codon