Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| ENERGY Form of engery |  | EVENT Abstract description of event involving energy |  | ENERGY SOURCE | CONDITION A condition that must be satisfied |  | CONSEQUENCE The result of the energy source, given the condition |
| --- | --- | --- | --- | --- | --- | --- | --- |
| a magnetic field | can | attract iron | ; for example, if | a permanent magnet | is near a steel nail | then | the nail will move towards the magnet |
| electrical energy | can | be changed to sound energy | ; for example, if | an electrical signal | enters the speaker of a telephone | then | the speaker will convert the electrical signals into speech |
| electrical energy | can | produce light and sound | ; for example, if | a bolt of lightning | strikes a tree | then | there will be a bright flash and a loud noise |
| electricity | can | be converted to light | ; for example, if | a battery | is connected with wires to a light bulb | then | the bulb will glow with light |
| friction | can | cause heat | ; for example, if | a speeding car | skids its tires on a road | then | the skidding will cause the tires to become hot |
| friction | can | slow an object moving along a surface | ; for example, if | a rolling ball | is moving on flat ground | then | the ball will slow and eventually halt |
| friction | can | slow an object moving along a surface | ; for example, if | a rolling ball | is rolling through thick grass | then | the ball will slow and quickly come to a halt |
| gravity | can | pull one object towards another | ; for example, if | a person | throws a ball up into the air | then | the Earth will pull the ball back down |
| gravity | can | pull an object downwards | ; for example, if | a marble | is dropped into a glass of water | then | the marble will fall to the bottom of the glass |
| gravity | can | pull an object downwards | ; for example, if | a ball | is released in the air with no support | then | the ball will fall to the ground |
| gravity | can | pull an object downwards | ; for example, if | a rock | is released at the top of a hill | then | the rock will roll down the hill |
| heat energy | can | be transferred from one location to another | ; for example, if | a stove | heats a kettle of water | then | the heat will move from the stove to the water |
| heat energy | can | be changed to sound energy | ; for example, if | a kettle with a whistle | is used to boil water | then | the kettle will make a whistling sound as the steam from the boiling water escapes from the kettle's spout |
| high friction | can | cause an object to move slow | ; for example, if | a bicycle | is moving on a rough road | then | the bicycle will move slowly |
| light | can | cause heat | ; for example, if | bright sunlight | shines on asphalt | then | the asphalt will become hot |
| light energy | can | be reflected by an object | ; for example, if | a flashlight | shines on a mirror | then | the light from the flashlight will bounce off the mirror |
| light energy | can | be changed to sound energy | ; for example, if | a radio wave | is received by a radio | then | the radio will convert the radio wave into sound |
| low friction | can | allow an object to move fast | ; for example, if | a bicycle | is moving on a smooth road | then | the bicycle will move fast |
| magnetic energy | can | produce motion | ; for example, if | a compass needle | is allowed to rotate freely | then | the compass needle will turn until it points north |
| magnetism | can | cause motion | ; for example, if | a magnet | is waved near a pile of steel nails | then | the nails will move |
| magnetism | can | attract iron | ; for example, if | a magnet | is moved towards a pile of iron nails | then | the nails will move as the magnet comes closer |
| mechanical energy | can | be converted to sound energy | ; for example, if | a pianist | strikes a piano key | then | the piano will make a musical sound |
| mechanical energy | can | be used to move something from on location to another | ; for example, if | a worker | applies a shovel to a pile of dirt | then | the dirt will move |
| mechanical energy | can | be used to move something from on location to another | ; for example, if | a baseball player | throws a baseball | then | the baseball will move away from the player |
| mechanical energy | can | be changed to sound energy | ; for example, if | a baby | shakes a rattle | then | the rattle will make a noise |
| mechanical energy | can | produce motion | ; for example, if | a person | pushes a wooden block on a floor | then | the block will move across the floor |
| motion of a liquid against a solid | can | cause erosion of the solid | ; for example, if | the ocean's waves | are pounding against the coast | then | the waves will wash away some of the coastal soil |
| sound | can | cause vibration | ; for example, if | a lound sound | occurs near a wooden door | then | the door will vibrate |
| sound energy | can | move through air | ; for example, if | two people | are having a converstation at a table | then | sound is moving through the air between them |
Question:
"When a marble drops into a glass and sinks to the ground,what keeps it down?" Select the correct choice to answer the question or fill in the blank.
Choices:
(A) Gravity
(B) light
(C) low friction
(D) magnetism
Answer:
(A) Gravity