Which term describes an observable fact, event, or circumstance? A. Experiment
B. Theory
C. Hypothesis
D. Phenomenon

Phenomenon

Explanation:

phe·nom·e·non

/fəˈnäməˌnän/

noun

1.

a fact or situation that is observed to exist or happen, especially one whose cause or explanation is in question:

"glaciers are unique and interesting natural phenomena"

synonyms

occurrence, event, happening, fact, situation, etc.

2.

a remarkable person, thing, or event:

"the band was a pop phenomenon just for their sales figures alone"

synonyms

marvel, sensation, wonder, prodigy, miracle, etc.

wavelength variability is the right one

the displacement produced by the body.  

the amount of force subjected to the body.  

the angle between the direction of force and displacement