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: the sahel is a narrow belt of land in west africa.

SOLUTION: sahel

PROBLEM: the chinese postman problem is a mathematical problem of graph theory.

SOLUTION: chinese postman problem

PROBLEM: information systems (is) is the study of how people put data into computers to create useful information.

SOLUTION:
information systems