What are the keywords in the following sentence? hidden behind a blade of grass
blade, grass, hide

What are the keywords in the following sentence? A group of firemen sit at the fire station idly.
fireman, sit, station

What are the keywords in the following sentence? public transport bus stopped at the bus stop to pick up passengers .
bus, passenger, pick, stop

What are the keywords in the following sentence? port of shipyard with heavy lifting cranes and a ship waiting to off load its cargo
cargo, crane, load, ship