Option 1: (C), (B), (A), (D) -> This breaks the logical flow as (B) appears before establishing what the disadvantages would be.
Option 2: (D), (B), (A), (C) -> Starting with (D) lacks a proper subject introduction, making the sentence incomplete.
Option 3: (D), (A), (B), (C) -> Similar issue - begins without establishing the main subject clearly.
Option 4: (C), (A), (D), (B) -> Forms a complete sentence: "A world where everyone speaks English and only English would have advantages but also major disadvantages for it would be a duller, blander world with everyone engaged in the same kind of conversations making us lose a huge amount of diversity and uniqueness in the world."
Hence, Option 4: (C), (A), (D), (B) -> This arrangement logically introduces the subject (a world with only English), acknowledges both sides (advantages and disadvantages), describes the negative outcome (duller world), and concludes with the broader consequence (loss of diversity) -> correct