Read each sentence to find out whether there is any grammatical or idiomatic error in it. The error, if any, will be in one part of the sentence. The corresponding letter of that part is the answer. If the given sentence is correct as it is, then choose option ‘No error’ as your answer response. (Ignore errors of punctuation, if any).

A Ramsar site is a (A)/ wetland designated to (B)/ be of international importance (C)/ over an environmental Treaty. (D)

Correct option is D

The preposition "over" is incorrect in this context. The correct preposition is "under" because it indicates that the Ramsar site is designated in accordance with the provisions of the treaty.
The correct sentence should be: "A Ramsar site is a wetland designated to be of international importance under an environmental treaty."
Rule: Use "under" to indicate conformity with a rule, regulation, or treaty. Here, "under" correctly specifies that the designation is according to the environmental treaty.