Final answer:
To inspect an infant's ear canal and tympanic membrane, the earlobe should be pulled downward and back to straighten the ear canal.
Step-by-step explanation:
When inspecting the external ear structures of an infant, particularly when trying to get a clear view into the ear canal and tympanic membrane, one must position the ear appropriately. The correct method for infants involves pulling the earlobe downward and back. This motion is necessary because the ear canal of an infant is different from that of an adult, and this technique helps to straighten the canal for better visualization.