TASK DEFINITION: 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.
PROBLEM: ammonium carbonate, also known as baker's ammonia or sal volatile, is a chemical compound.

SOLUTION: ammonium carbonate

PROBLEM: landing craft are small or medium sized boats.

SOLUTION: landing craft

PROBLEM: bielefeld is a city in the north-west of germany, in the state of north rhine-westphalia.

SOLUTION:
bielefeld