Option 1: (A), (C), (B), (D) -> Creates logical flow: "if life exists on Mars, it is most likely to be in the form of bacteria buried deep in the planet's permafrost or lichens growing within rocks, say scientists from NASA"
Option 2: (A), (B), (C), (D) -> Breaks the natural connection between "most likely" and "to be in the form of bacteria"
Option 3: (B), (A), (D), (C) -> Starts with a prepositional phrase without context, creating an incomplete and illogical sentence
Option 4: (C), (B), (D), (A) -> Begins with an infinitive phrase without proper subject, making the sentence grammatically incorrect
Hence, Option 1: (A), (C), (B), (D) -> The sentence flows logically with the conditional clause first, followed by the main prediction about bacteria, then specific locations (permafrost/lichens), and concludes with the attribution to NASA scientists -> correct