共用题干

共用题干
An Expensive Mistake
Is there water on the planet Mars?Is there life in Mars? Was there ever life on Mars? Scientists from NASA wanted to know the answers to these questions.They built a space-craft to travel around Mars and get information.The spacecraft was called the Mars Climate Orbiter.
The Mars Climate Orbiter left for Mars in December 1998.The trip took nine and a half months.At first,everything was fine.However,when the Orbiter got near Mars,something terrible happened.The spacecraft didn't go to the right place.It went too close to Mars.It was too hot for the Orbiter there.The spacecraft couldn't function correctly.Suddenly,it stopped sending messages to NASA.The Orbiter was lost.
How could this terrible thing happen? How did the Orbiter get closer to Mars than the scientists planned?Finally,they found the answer.Two teams of scientists worked together on the Orbiter.One team was in England,and one team was in United States.There were many similarities in the way they worked,but there was one important difference:The teams used different guidelines for measuring things.The United States team used the metric system（公制）.The other team used the English system.
Because they used different systems,the scientists made a mathematical mistake.The Orbiter's orbit(the shape and pattern of its path)around Mars was not correct.The scientists put the Orbiter on the wrong path.The Orbiter got too close and too hot.And it stopped functioning.
Why didn't anybody see the mistake before it was too late? Many things contributed to the problem.One thing was that NASA scientists and mathematicians were working on two other spacecrafts at the same time.This was a challenge,and they were very tired from working long hours.
The Mars Climate Orbiter cost$94 million to build.It also cost a lot of money to try to find the lost Orbiter in space.In addition,NASA's research on the cause of the problem was very expensive.This wasn't the first time that two different measurement systems caused mistakes in scientific projects.However,the Mars Climate Orbiter was definitely the most expensive mistake of all!

What caused the Orbiter's problem,______.
A:Scientists used wrong guidelines of mathematics
B:Scientists used wrong building materials
C:Scientists used different operating systems
D:Scientists used different measurement systems