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Astronauts Christina Koch and Jessica Meir made history on Friday when they climbed into spacesuits and left the International Space Station to perform a spacewalk. It was the first time a spacewalk has been conducted by two women.

A spacewalk， in this case， is when astronauts go outside the International Space Station. Usually， spacewalks are done to make repairs or do maintenance work.

The two astronauts needed to swap out a large battery that had failed. They replaced it with a new one. Koch and Meir are two of six astronauts who are currently living and working in space on board the International Space Station. It was Koch's fourth spacewalk （she has spent a total of 27 hours， 48 minutes on spacewalks）. It was Meir's first spacewalk. Koch and Meir began their spacewalk at 7：50 a.m. It lasted seven hours and 17 minutes.

Every aspect of the job is done slowly and carefully， with nothing left to chance. NASA's controllers on Earth even knew how many turns of the screwdriver it would take to undo or replace each screw.

The spacewalk was streamed live on NASA's YouTube channel， with Brandi Dean， NASA's public affairs director， explaining what the astronauts were doing and answering questions posted on Twitter.

Astronauts train on Earth for spacewalks in a “neutral buoyancy lab”， which is an enormous swimming pool with a mock-up of the space station in it. Astronauts also train using virtual reality and use a system with pulleys that makes it feel like they're in micro-gravity， Dean said.

The astronauts wore space suits that are bulky; they would weigh about 300 lbs on Earth. The suits act as a type of “personal space station”， a NASA representative said on the live stream.

It took the pair three and a half hours to swap out the battery unit. The astronauts then performed other maintenance tasks as well.

根據(jù)短文內(nèi)容，選擇最佳答案。

1. Why were Astronauts Christina Koch and Jessica Meir reported to make history？

A. Because it was their first time to perform a spacewalk.

B. Because the task they completed was extremely challenging.

C. Because they became the first women to work in the International Space Station.

D. Because they were the first females to have conducted a spacewalk without males.

2. Which of the following can replace the underlined phrase “swap out” in Paragraph 3？

A. Change. ? ? B. Repair. ? ? C. Unload. ? ? D. Turn out.

3. What do we know about these two women's spacewalk on Friday？

A. It started at 8 sharp in the morning.

B. It came to an end at 15：07 the next day.

C. It was broadcast live on TV and the Internet.

D. It was carefully planned and prepared by NASA.

4. What does the author intend to do in the 6th paragraph？

A. Add some background information. B. Introduce a new topic for discussion.

C. Explain how they were chosen out. D. Summarize the previous paragraphs.