Which sentence is best structured to present two ideas of equal importance?
A. Since NASA was founded, it has sent more than 250 astronauts
into space.
B. NASA is known for sending humans to the moon, but the famous
space program has also sent an unmanned spaceship to Mars.
O C. The mission of NASA is to explore outer space.
D. 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.
