NASA astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko headed back toward the Earth on Tuesday after nearly a year aboard the International Space Station, ending a record-long US spaceflight intended to pave the way for human travel to Mars.Kelly and Kornienko have been aboard the space station for 340 days, about twice as long as previous crews. Their flight sets a record for the space station and for the longest US space mission.Throughout their nearly year-long stay in space, Kelly, 52, and Kornienko, 55, have been the subjects for dozens of medical experiments and science studies designed to learn more about how weightlessness and the high radiation environment of space impact the human body.The research is intended to help the US space agency and its partners develop plans for eventual human missions to Mars that will last at least two years.1.What is the news report mainly about?A) The space station ends the acceptance of travelers from the Earth.B) A new satellite will be launched by the NASA to Mars this Tuesday.C) NASA is going to start a-year-long space exploration mission to Mars.D) Astronauts return to the Earth after a year’s work in the space station.2.What is the final purpose of the space research mentioned in the news?A) To carry out medical experiments on Mars.B) To study how weightlessness affects human body.C) To keep space radiation from penetrating to the Earth.D) To help humans plan missions to Mars.