Question 4.

Let us evaluate the choices individually:

Option A: [the number of chromatophores in Cephalopods is half the number of iridophores and leucophores] If true, this does not undermine the camouflaging adeptness of Cephalopods primarily because each of chromatophores, iridophores and leucophores have specific [somewhat independent] roles to play and it is unclear how their quantity would directly impact the camouflaging capacity. Even if the number of chromatophores is fewer than the other types, the octopus can still maintain its camouflaging adeptness.  

Option B: [the temperature of water at the depths at which Cephalopods reside renders the transmission of neural signals difficult.] If true, this would limit the camouflaging adeptness primarily because the underlying mechanism is being restricted/impacted.  {When the cephalopod wants to change colour, the brain carries an electrical impulse through the nerve to the muscles that expand outwards, pulling open the sacs to display the colours on the skin.}

Option C: [light reflects the colours red, green, and yellow at the depths at which Cephalopods reside.] If true, this would limit the camouflaging adeptness primarily because the underlying mechanism is being restricted/impacted. If the colour scheme is distinct, it would undermine the observations presented below: {[Chromatophores] are organs on their bodies that contain pigment sacs, which have red, yellow and brown pigment granules...Why these three colours? Because these are the colours the light reflects at the depths they live in (the rest is absorbed before it reaches those depths)}

Option D: [the hydrostatic pressure at the depths at which Cephalopods reside renders radial muscle movements difficult.] If true, this would limit the camouflaging adeptness primarily because the underlying mechanism is being restricted/impacted. {These sacs have a network of radial muscles, meaning muscles arranged in a circle radiating outwards.}

Hence, Option A is the correct choice.