Rules around here are pretty lax but for me 'a sense of scale' would involve 2 or more focal points in an image.

At least one of the focal points should be significantly larger or smaller than the other focal point so that 'scale' is an important and obvious part of the image.

An easy example would be a mountain climber, climbing a mountain where the large mountain dwarfs the person climbing it, and thus the scale of the mountain relative to the climber is an important and obvious part of the image.

(Of course you are free to bust open my definition and interpret this as you wish.)

Hope that may help and thx for posting these assignments yesterday.