What are the keywords in the following sentence? an organ is a structure made of a group of tissues working together to perform specific functions
function, structure, tissue

What are the keywords in the following sentence? time lapse of clouds floating over a mountain during the day
cloud, day, mountain

What are the keywords in the following sentence? This train is parked under a bridge and stairwell.
bridge, park, train

What are the keywords in the following sentence? a lighthouse shines out to sea to warn passing boats and ships
boat, pass, sea, ship