What are the keywords in the following sentence? color image of some very old religious paintings on a wall
image, painting, wall

What are the keywords in the following sentence? The friends bought the gift collectively.
buy, friend, gift

What are the keywords in the following sentence? A train is parked on abandoned track in the grass.
abandon, grass, track, train

What are the keywords in the following sentence? chemical element is number in the periodic table
element, number, table