Statement: "Please use the stairs if the elevator is crowded; it is a healthy alternative and saves electricity." — A notice posted in a 10-story office building. Assumptions:
I. The people reading the notice are physically capable of using the stairs.
II. The elevator in the building frequently becomes crowded.
III. Using stairs is beneficial for physical health.

Assumption I is implicit because a public notice requesting an action assumes that the target audience has the ability to perform that action. Assumption II is implicit because the notice specifically addresses the condition "if the elevator is crowded," which implies that this is a recognized or expected occurrence in the building. Assumption III is implicit because the statement itself justifies the suggestion by calling it a "healthy alternative," taking for granted that stair-climbing provides health benefits. Hence, option D.