Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

Ex Input:
a releaser is a stimulus from one animal to another, which causes a particular response.

Ex Output:
releaser


Ex Input:
henry's marriage to catherine of aragon was finally annulled in the following may by archbishop cranmer, thus ending the first of henry's 6 marriages.

Ex Output:
catherine of aragon


Ex Input:
a visit to the nursery is an oil painting by jean-honoré fragonard.

Ex Output:

a visit to the nursery