The correct option is B Amoeba
Amoeba is a unicellular organism i.e., it is made up of a single cell. This single cell performs all the essential life processes by itself. Therefore, any injury to this cell can be fatal and even lead to death. Horses, snails and humans on the other hand are multicellular organisms. They are made up of many cells. Any injury to one of the cell of these organisms would not lead to any significant disruption in essential life processes.