Final answer:
The correct option is a. An increased frequency of urination is termed pollakiuria, which differs from polyuria, the production of a large volume of urine. Both are distinct from oliguria and anuria, which involve low and no urine output, respectively.
Step-by-step explanation:
When an animal exhibits an increased frequency of urination, it is essential to distinguish between the frequency of urination and the volume of urine produced. The term for increased frequency of urination is pollakiuria. This is different from polyuria, which refers to an abnormally large amount of urine, often exceeding 2.5 L/day and associated with conditions like diabetes insipidus, diabetes mellitus, or excessive use of diuretics.
On the other hand, conditions like oliguria, where the output is abnormally low (less than 600 ml/day), or anuria, where there is a complete absence of urine (below 10 ml/day), are also important to recognize due to their potential severity and underlying causes.