Read the following passage and choose the correct answer (A, B, C or D) to each of the questions.           

               Physicists are scientists who study the physical world. They study matter, the “stuff” that makes up all things. They study forces and how things move. They study atoms. They study stars and space. They also study energy and how it changes forms. Physicists do experiments. They observe what happens. They use math to find the answers to questions. They use computer models to study things. Some physicists study the universe to find out how it began. Some try to solve practical problems right here on Earth. They might invent new machines or new materials. Physicists often work in labs. Some may teach at colleges. Some work for the government. Some work in hospitals or medical services. If you’d like to be a physicist, you'll need to take many math and science courses in high school and college. You should be good at solving problems. You'll need curiosity, too!

 What does a physicist do?