12月18日，南昌上空碧空如洗。南昌连续三日空气质量指数（AQI）在50左右，空气优良。加上天气晴暖，市民们纷纷来到室外享受这久违的冬日暖阳。但要留住“南昌蓝”，我们还需要做出更多的努力。人类这么重视“天空的蓝”，是因为（      ）

    It is Sunday today but my three good friends are not at home. Tina is at the mall. Is she shopping? No, she isn't. She is eating lunch with one of her friends. Mike is still at school. Is he doing his homework? No, he isn’t. He's playing basketball with other boys. What about Lisa? Where is she? She is at the library. She is reading a book. Is it an interesting book? Yes, it is. Lisa likes this book very much.

1960年11月，中共中央下发了《关于农村人民公社当前政策问题的紧急指示信》，规定：允许社员经营少量的自留地和小规模家庭副业……在不影响集体劳动的情况下，鼓励社员种好自留地，饲养少量的猪、羊和家禽……有引导有计划地恢复农村集市。这表明（     ）