What are the keywords in the following sentence? traveling in a car with their luggage tied on top .
car, luggage, travel

What are the keywords in the following sentence? A cat on the lid of a toilet looking perturbed.
lid, look, toilet

What are the keywords in the following sentence? charged atoms the number of protons determines the element .
atom, element, number, proton

What are the keywords in the following sentence? An airplane flies over a city in the day.
airplane, day, fly