Which sentence is best structure to combine ideas of equal importance when they include a least one unequal element A. The mission of NASA is to explore outer space. B. Since NASA was found it it has sent more than 250 astronauts into space. C. 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 go, even though it will be difficult. D. NASA is known for sending humans to the moon, but the famous space program has also sent an unmanned spaceship to Mars.