In which of the following situation work is being done?

• Work is done when a force acts upon an object to cause a displacement. 
• A boy pushing a wall doesn't cause the wall to move. So, there was no work done.
• When a coolie holds luggage or when a student holds a book,  there is no displacement because there is no force acting against gravity. Therefore, no work is done.
• When a girl climbs stairs, she applies force against gravity and moves higher as well, i.e. there is a displacement in the force's direction. Hence, work is done.

Therefore, 'A girl climbing up the staircase.' is the correct response.