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.

Example Input: sandpaper is a piece of paper with an abrasive glued to it.
Example Output: sandpaper

Example Input: the boiling point of a substance is the temperature at which the substance boils, or enters a state of rapid evaporation.
Example Output: boiling point

Example Input: deer are a group of even-toed ungulate mammals.
Example Output:
deer