What are the keywords in the following sentence? stacks of books bound together on an old shelf
bind, book, stack

What are the keywords in the following sentence? An airplane sits on a runway in a airport
airplane, airport, runway, sit

What are the keywords in the following sentence? boys sit at the ruins of the mosque before offering prayers on the occasion
mosque, prayer, sit

What are the keywords in the following sentence? the earth in space and the moon
earth, moon, space