What are the keywords in the following sentence? an aircraft flies high over region on a training mission
aircraft, fly, region

What are the keywords in the following sentence? book with a trees in the shape of heart
book, heart, tree

What are the keywords in the following sentence? cantilever bridge is part of streets .
bridge, cantilever, part

What are the keywords in the following sentence? satellite captured this ultraviolet image of the moon eclipsing the sun .
capture, moon, satellite, sun