D is correct

honeysn wrote:The proposed urban development zones do not
represent a new principle; it was employed in
"Operation Bootstrap" in Puerto Rico.

(A) do not represent a new principle; it - 'it' is wrong. Subject is 'zones', so we need plural verb
(B) represent not a new principle, but one that - wordy and lacks working verb
(C) are not a new principle; the same one - semicolon is not required
(D) are not a new principle, but one that - Not X but Y, correct
(E) are not new in principle; it - Same as A

OA for this is B

Kindly help to crack this one ...

"The proposed urban development zones" are'nt a new principle but represent one. Hence C,D and E are out. This sentence also implies a contrast.For eg. X is not Y but is equal to Z. The option A violates this.Also "zones" is plural and hence "it" cannot be used. No errors are evident in B,though "represent not a new principle" sounds awkward,it is the best of the options.