One student did an experiment with sand, rocks, pebbles, and water. The steps of the experiment are shown below.
Cut out the bottom of a two liter plastic bottle.
Remove the cap of the bottle and fix a loosely woven cotton cloth on the mouth of the bottle with the help of a tape.
Fix the cap tightly on the cotton cloth.
Put a cup of sand into the bottle through the opening cut out at the bottom.
Pour water slowly into the bottle.
Open the cap and observe how the water flows out of the bottle through the cotton cloth.
Empty the bottle and replace the cap.
Repeat the experiment by putting a layer of rocks, pebbles and sand in the bottle.

What does the student's experiment most likely demonstrate?

Select one:
a. groundwater reacts with sand, rocks, and pebbles
b. groundwater corrodes sand, rocks, and pebbles to form caverns
c. groundwater causes layers of sand to collapse and form sinkholes
d. groundwater moves at different rates through different layers of the Earth