对于某酸性溶液（可能含有Br^﹣、SO₄ ^2﹣、HSO₃^﹣、NH₄⁺ ），分别进行如下实验：①加热时放出的气体可使品红溶液褪色；②加入碱溶液使溶液呈碱性，再加热时放出的气体可使湿润的红色石蕊试纸变蓝；③加入氯水时，溶液略呈橙红色；④加入BaCl₂液和稀硝酸，产生不溶于稀硝酸的白色沉淀．对于下列微粒不能确定其在原溶液中是否存在的是（　　）

①要在发挥主观能动性的基础上尊重客观规律

②要抓住时机实现事物的飞跃和发展

③要善于在矛盾的斗争性中把握矛盾的同一性

④要学会统筹考虑以实现最优目标

王国维《宋元戏曲考》称：“凡一代有一代之文学……唐之诗、宋之词、元之曲，皆所谓一代之文学，而后世莫能继焉者也。”下列属于“宋之词”代表人物的是（    ）

    In the past black people in South Africa ____(live) a miserable life. They could not vote to choose their ____(leader). They could not get jobs they wanted. The parts of town in which they had to live ____ (decide) by white people. They lived in the ____(poor) areas in the country and could not get jobs they wanted. Nelson Mandela, a modern hero, called black people ____ fight against white people to make black and white people equal. He said “We were put in a position ____we had either to accept we were less important,____ fight the Government. We chose to attack the law. We first broke the law____a way which was ____(peace); when this was not allowed…only then ____we decide to answer violence with violence.”

Mary has many nice dresses. She wears a different one every day        the week.