If something happens to alter the quantity demanded at any given price, then a. the demand curve becomes steeper. b. the demand curve becomes flatter. c. the demand curve shifts. d. we move along the demand curve.

C. the demand curve shifts.

Step-by-step explanation:

If quantity demanded changes at any given price, there is a shift (right or left) from any given price. Graphically, this is a shift in the demand curve itself.

Figure:

based on context clues you gave i'm assuming the answer would be c.