The difficulty of reading under dim light conditions can be explained by
a. the increased sensitivity of cones under low light conditions
b. the increased acuity of cones under low light conditions
c. the fact that rod functioning predominates during dark adaptation, resulting in poor acuity
d. the fact that cone functioning predominates during dark adaptation, resulting in poor acuity

c) the fact that rod functioning predominates during dark adaptation, resulting in poor acuity

Explanation:

In  dim light conditions the dark-adapted (scotopic) visual subsystem operates. Rods are responsible for the initiation of this process, they are more sensitive to light but has poor acuity and are  color insensitive. Hence it is difficult to identify details.  

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