Dưới đây là các từ đã được chọn vào chỗ trống:

1. Sputnik 1, the first artificial satellite, was **launched** into Earth orbit on 4 October 1957.
2. NASA prepares its astronauts for a microgravity environment by **training** them on parabolic flights.
3. A mysterious spacecraft has **orbited** the Earth for the past 720 days.
4. It took less than an hour before the plane began **descending** down to a small town.
5. Astronauts **float** around in space because there is no gravity in space.

Nếu bạn cần thêm hỗ trợ, hãy cho tôi biết!