Final answer:
The combining form that indicates deficiency is 'oligo/'. It is used in various medical terms to denote a lesser than normal quantity, such as in oliguria, which is low urine output.
Step-by-step explanation:
The combining form that means deficiency is d. oligo/. This prefix is used in medical terminology to indicate a reduced quantity or fewness in number. For example, oliguria refers to below normal urine production of 400-500 mL/day, signifying a deficiency in urine output. Other medical terms that use 'oligo-' to imply deficiency include oligospermia (low sperm count) and oligomenorrhea (infrequent menstrual periods).