Option 1 -> Starts with a location phrase "across northern Africa..." which cannot begin the sentence logically.
Option 2 -> Forms a complete, coherent sentence: "The Sahara Desert is the largest hot desert in the entire world covering approximately 9.2 million square kilometers across northern Africa's vast arid regions."
Option 3 -> Begins with a participle phrase "covering..." without establishing the subject first, making it grammatically incorrect.
Option 4 -> Places "hot desert in the entire world" at the end, breaking the logical flow and separating it from "the largest" which it should follow.
Hence, Option 2: (C), (A), (B), (D) -> This arrangement creates a grammatically correct and meaningful sentence that introduces the subject (The Sahara Desert), establishes its status (largest hot desert), provides specific data (9.2 million square kilometers), and concludes with its location (across northern Africa) -> correct