A 19-year-old woman with no significant past medical history comes in for a pre-college physical examination required by her school. She has no complaints, and her review of systems is negative. Her temperature is 37.0°C (98.6°F), blood pressure 120/80 mm Hg, pulse 80/min, and respirations 10/min. Physical examination reveals a single nodule on the left lobe of the thyroid gland. Her thyroid-stimulating hormone is within normal limits.

Which of the following is the most appropriate next step in management?
1) Observation and repeat thyroid-stimulating hormone level in 6 months
2) Fine-needle aspiration biopsy
3) Radioactive iodine uptake scan
4) Thyroid ultrasound