Over the next 20 years, we are going to send more and better robots to Mars. Those robots will send back better pictures, maps, samples, and weather reports. There is a limit to what robots can tell us, though, so eventually we will have to send people to study the planet. Before people can visit Mars, we need to invent a spaceship that can take us there. Mars is very far away. Depending on where Mars and Earth are in their orbits around the sun, it could take between six months to a year to get there. The moon is much closer, and we were there, 25 years ago. Over the next 10 years, we are going to work on building a new spacecraft that can go to the moon. Using this craft, we will practice the skills we need to go to Mars. Once we return to the moon, we are going to build a station so that people can live and work on the moon for months at a time. This is important so that we have a place to start from when we want to visit Mars, but it is also important because it gives us practice  with living away from Earth. By the time you are old enough to be an astronaut, we will have people spending months on the moon. By the time you are old enough to be a commander of a space mission, we will be taking trips to Mars. By the time your kids are old enough to be astronauts, we may have people living on Mars. Wouldn't it be cool to get a postcard from someone who was building a house on Mars? Wouldn't it be cooler if it was you who sent the postcard? We eventually have to send people on Mars because  _  .
robots could not send back pictures robots can't tell us all we want to know robots are controlled by us humans robots are no longer of any use to us
Question: Over the next 20 years, we are going to send more and better robots to Mars. Those robots will send back better pictures, maps, samples, and weather reports. There is a limit to what robots can tell us, though, so eventually we will have to send people to study the planet. Before people can visit Mars, we need to invent a spaceship that can take us there. Mars is very far away. Depending on where Mars and Earth are in their orbits around the sun, it could take between six months to a year to get there. The moon is much closer, and we were there, 25 years ago. Over the next 10 years, we are going to work on building a new spacecraft that can go to the moon. Using this craft, we will practice the skills we need to go to Mars. Once we return to the moon, we are going to build a station so that people can live and work on the moon for months at a time. This is important so that we have a place to start from when we want to visit Mars, but it is also important because it gives us practice  with living away from Earth. By the time you are old enough to be an astronaut, we will have people spending months on the moon. By the time you are old enough to be a commander of a space mission, we will be taking trips to Mars. By the time your kids are old enough to be astronauts, we may have people living on Mars. Wouldn't it be cool to get a postcard from someone who was building a house on Mars? Wouldn't it be cooler if it was you who sent the postcard? We eventually have to send people on Mars because  _  .
A. robots could not send back pictures
B. robots can't tell us all we want to know
C. robots are controlled by us humans
D. robots are no longer of any use to us
Answer: