Astronauts have already visited the Moon and lived on space stations．They've never been to another planet，but they might visit Mars soon．Astronauts will spend about six months getting to the pla
When I get older, I will be stronger. They’ll call me ______. Just like a _____ flag. A. free; wave B. freedom; to wave C. free; waved D. freedom; waving
是虚数单位，则复数
在复平面内对应的点位于第 象限。