Final answer:
The correct term for a flexible, spiral-shaped bacterium is 'spirochete.' This shape is distinct from other bacterial shapes such as cocci, bacilli, and spirilli.
Step-by-step explanation:
A flexible, spiral-shaped bacterium is commonly referred to as a spirochete. This term is used to identify bacteria that have a distinct spiral shape and are often associated with the genus Spirochaeta, which includes well-known organisms such as those causing Lyme disease and syphilis. The correct answer to the student's question is A) spirochette, which is distinctive from other bacterial shapes like cocci (spherical), bacilli (rod-shaped), spirilli (also spiral-shaped but thicker than spirochetes), and vibrios (comma-shaped).