What are the keywords in the following sentence? tourists relaxing on a cruise ship at sea
sea, ship, tourist

What are the keywords in the following sentence? passengers await the arrival of a subway train at station .
arrival, await, passenger, station, train

What are the keywords in the following sentence? They continue their journey through the rough water of the rapids.
journey, rapid, water

What are the keywords in the following sentence? patch of green lichen growing on the trunk of a deciduous tree in a circular pattern
grow, pattern, trunk