Which of the following organisms has the largest surface area-to-volume ratio?

Amoeba has the largest surface area-to-volume ratio among the organisms listed. This is because amoebas are unicellular organisms with a relatively large surface area compared to their volume. Since their shape is irregular and constantly changing, they can increase their surface area by extending and retracting pseudopodia. This allows them to take in nutrients and oxygen from their environment and expel waste products more efficiently. In contrast, larger organisms such as man, earthworm, and grasshopper have much smaller surface area-to-volume ratios due to their larger sizes and more complex body structures. Therefore, the correct answer to the question is Amoeba.