Critical Reasoning

Damaged nerves in the spinal cord do not regenerate themselves naturally, nor even under the spur of nerve-growth stimulants. The reason, recently discovered, is the presence of nerve-growth inhibitors in the spinal cord. Antibodies that deactivate those inhibitors have now been developed. Clearly, then, nerve repair will be a standard medical procedure in the foreseeable future.
Which of the following, if true, casts the most serious doubt on the accuracy of the prediction above?

(A) Prevention of the regeneration of damaged nerves is merely a by-product of the main function in the human body of the substances inhibiting nerve growth.
(B) Certain nerve-growth stimulants have similar chemical structures to those of the antibodies against nerve-growth inhibitors.
(C) Nerves in the brain are similar to nerves in the spinal cord in their inability to regenerate themselves naturally.
(D) Researchers have been able to stimulate the growth of nerves not located in the spinal cord by using only nerve-growth stimulants.
(E) Deactivating the substances inhibiting nerve growth for an extended period would require a steady supply of antibodies.

IMO (E)

A) Prevention of the regeneration of damaged nerves is merely a by-product of the main function in the human body of the substances inhibiting nerve growth.
This implies that there are many fiunctions of this substance apart from inhibitiion....So every time there is a procedure doctors should take care that other functions should not get affected and hence doctors cannot do the same thing for every patient evrytime. It will depend from patient to patient.

(B) Certain nerve-growth stimulants have similar chemical structures to those of the antibodies against nerve-growth inhibitors.
irrelevant

(C) Nerves in the brain are similar to nerves in the spinal cord in their inability to regenerate themselves naturally.
irrelevant

(D) Researchers have been able to stimulate the growth of nerves not located in the spinal cord by using only nerve-growth stimulants. no effect on conc......

(E) Deactivating the substances inhibiting nerve growth for an extended period would require a steady supply of antibodies.
may or may not inhibit the procedure become standard

IMO A

gmatnmein2010 wrote:Damaged nerves in the spinal cord do not regenerate themselves naturally, nor even under the spur of nerve-growth stimulants. The reason, recently discovered, is the presence of nerve-growth inhibitors in the spinal cord. Antibodies that deactivate those inhibitors have now been developed. Clearly, then, nerve repair will be a standard medical procedure in the foreseeable future.
Which of the following, if true, casts the most serious doubt on the accuracy of the prediction above?

(A) Prevention of the regeneration of damaged nerves is merely a by-product of the main function in the human body of the substances inhibiting nerve growth.
(B) Certain nerve-growth stimulants have similar chemical structures to those of the antibodies against nerve-growth inhibitors.
(C) Nerves in the brain are similar to nerves in the spinal cord in their inability to regenerate themselves naturally.
(D) Researchers have been able to stimulate the growth of nerves not located in the spinal cord by using only nerve-growth stimulants.
(E) Deactivating the substances inhibiting nerve growth for an extended period would require a steady supply of antibodies.

(A) is correct as it is clearly mentioned that 'prevention of the regeneration of damaged nerves is merely a by-product of the inhibitors'.. which leads us to presume that these inhibitors perform some other main functions.. thus using antibodies which render these inhibitors inactive would affect some other functions primarily performed by the inhibitors. So it can't be followed as a standard medical procedure.