Final answer:
A mutation that changes the nucleotide sequence of the silencer will cause a constitutive synthesis of the lactose-utilizing proteins.
Step-by-step explanation:
The correct answer is d) Silencer. A mutation that changes the nucleotide sequence of the silencer will cause a constitutive synthesis of the lactose-utilizing proteins. The silencer is a DNA sequence that binds to a repressor protein and prevents it from binding to the operator site. When the repressor is unable to bind to the operator, RNA polymerase can freely transcribe the genes necessary for lactose utilization.