Which sentence is best structured to make a direct statement about one idea? A. NASA is known for sending humans to the moon, but the famous space program has also sent an unmanned spaceship to Mars, B. Some people think that NASA should focus on exploring the universe, but others believe that building a colony on the moon is the most important goal, even though it will be difficult. C. The mission of NASA is to explore outer space. O D. Since NASA was founded, it has sent more than 250 astronauts into space.