Recall the Application About Why People Walk Up Stairs but Not

Recall the Application about why people walk up stairs but not escalators to answer the following
question(s) .
-Walking up an escalator as opposed to standing still on an escalator makes sense if the _______ of walking is less than the _______ of walking.

A) marginal benefit; marginal cost
B) marginal cost; marginal benefit
C) marginal benefit; opportunity cost
D) marginal cost; opportunity cost