Answer: B) As something approaches an octopus, it shoots a cloud of ink.
A stimulus is something which brings physiological change in the internal or external environment of the organism. Sensitivity is the ability of an organism to respond to the external stimulus or stimuli. These changes are detected by the sensory receptors present in the different parts of the organism. A stimulus can be light, chemical, pressure, temperature and other living organism.
As something approaches an octopus, it shoots a cloud of ink is a physiological response of the octopus to an immediate threat. This immediate threat could be another marine predatory organism acting as a stimulus.