Which definition best describes the verb fluctuate?

• A. To constantly undergo changes
• B. To undulate
• C. To shift back and forth; to rise and fall
• D. To stay constant

Answer: (C)

Fluctuate means to vary in level or amount, often moving up and down or back and forth. The definition that describes shifting back and forth and rising and falling nails the idea precisely: you’re watching something not stay the same, but swing between higher and lower values. The other options are less exact: one suggests constant changes without specifying the up-and-down pattern, another is close but emphasizes a smooth wave-like motion rather than irregular variation, and the last is the opposite, describing no change at all. For example, stock prices can fluctuate, rising and falling over the day rather than staying constant.