What are the keywords in the following sentence? a caterpillar of butterfly on leaf
butterfly, caterpillar, leaf

What are the keywords in the following sentence? vegetable crops on the hilly fields .
crop, field, vegetable

What are the keywords in the following sentence? Several people in one location with outfits on and numbers on their chest.
chest, number, outfit

What are the keywords in the following sentence? A green training sitting on train tracks at a station.
sit, track, training