英语首字母填空： According to scientists,in 2020,two spacecrafts will f_to the moon w_four astrona
ts and six tons of building materials.The four astronauts will start to w_in the base in space.They will come back i_a week.Then a_four astronauts will go and keep on buildings.Each four-member group will stay for one week at a time.When the base is ready for use,astronauts will stay there for more than 180 days at a time.In 2024 astronauts should be a_to stay as long as they want in the base.