Final answer:
The medical assistant should place the tympanic membrane thermometer in the patient's ear to measure temperature, using infrared technology for a quick and accurate reading.
Step-by-step explanation:
When a medical assistant prepares to collect a patient's temperature via the tympanic membrane, the assistant should place the thermometer in the ear (Option C). This is because tympanic membrane thermometers are designed to measure the infrared energy emitted by the eardrum, similar to how infrared astronomy technology measures the temperature of stars and planets. This method is non-invasive and reflects the core body temperature quickly and accurately without the risk of cross-contamination.