The spinal cord and the brain together comprise of the central nervous system. The spinal cord functions as a relay center for the reflex activities. The first thing the frog feels at the time of dissection is the sense of pain, and one cannot record the exact physiological reaction of the body towards the test compound.
As when one impart any stimulus, the central nervous system reacts instantaneously and starts safeguarding and reflex actions by discharging some of the chemical components and eliciting the movements of the body. The result of what one obtains in such case would not be entirely because of the test compound.
Thus, in order to inhibit the influence of the central nervous system on the contraction of the muscle, the brain and spinal cord of the frog should be destructed.
The lac repressor prevents the lac genes in the DNA of E. coli from being expressed most of the time. The answer to your question is A. I hope this is the answer that you are looking for and it comes to your help.
