Topic: Pronoun (সর্বনাম),

Best Answer Explained in Below-:

The sentence presents a concern regarding the preservation of archaeological sites that are threatened by development. To fill in the blank appropriately, we need a phrase that introduces the specific group of archaeological sites being discussed, while also maintaining grammatical coherence and clarity.

Option C, "many of which," is the correct choice because it effectively creates a relative clause that links back to "archaeological sites." Here, "many" refers to a large number of those sites, and "of which" indicates possession or belonging, meaning many of these sites are threatened.

In contrast, option A, "of which many," disrupts the natural flow and is not grammatically correct in this context, as it incorrectly implies that "many" is the subject. Option B, "many of them," misplaces the focus since "them" does not clearly refer back to "archaeological sites," breaking the coherence. Option D, "which many," also does not work, as it creates confusion by not directly linking back to the noun it describes, leading to ambiguity about what "which" refers to.

Thus, "many of which" clarifies which specific sites are being threatened, making it the most logical and grammatically correct choice.