An astronaut's work may sound exciting, but living in space isn't as fun as you think. The website www.space.com lists the disadvantages of living in space. Here are some of them.
    When astronauts work outside the station during spacewalks, they have to wear special gloves. The gloves are very tight. They can hurt the astronauts' fingernails(手指甲) and even make them fall off.
    In space, you don't have many choices in what you eat. It's hard to get fresh fruits and vegetables. It is not OK to eat bread because it leaves crumbs(碎屑). Crumbs could fly around everywhere.
    In space, it is impossible to have a good shower because water can fly all over the ship and break the machines. Astronauts have to use a special water-shooting(喷水) gun and a washcloth.
    Astronauts lose their bone strength quickly during their stay in space. So far, there is no way to solve this problem. They do exercise while they're in space to try to keep their bones strong as long as possible.
    Perhaps the hardest part of life in space is the feeling of loneliness. Astronauts sometimes have to spend weeks and even months away from Earth. They miss their friends and families.

如图，四边形ABCD为⊙O的内接四边形，已知∠C=∠D，则AB与CD的位置关系是____．

①“补短板”要弥补市场调节的弊端，熨平经济波动起伏

②“补短板”要加强和完善社会保障，健全养老保险制度

③“兜底线”要缩小城市发展差距，实现经济的同步发展

④“兜底线”要加强特困群体的社会救助，提高低保标准

为了彻底废除封建剥削的土地制度，人民政府颁布了（   ）