range over or vary over?

[san2612]

1. Our biological clocks govern almost every aspect of our lives. Our sensitivity to stimuli _______ over the course of the day, and our ability to perform certain functions is subject to fluctuations. Consequently, there is a peak time for tasks such as making decisions: around the middle of the day.



A. modifies
　
B. ranges
　
C. varies
　
D. waves


I chose B but the answer is C. Do you think "range over" sounds better?

 

[SoothingDave]

No. It varies.

 

[emsr2d2]

It definitely varies. Remember that this is not a phrasal verb you're looking for. The verb is simply "to vary" followed by a time period "over the course of a day". It's not "to range over".