题目

阅读下面短文，在空白处填入1个适当的单词或括号内单词的正确形式。The long goodbyeWhy was it so difficult to agree on a Brexit (英国脱欧) deal?-The border and backstop.When does 【1】 (certain) become the worst condition at all? This fall, more than three years after Britain voted to leave the European Union, no one was sure what form Brexit would take, what kind of relationship they would have with the nearest neighbors, 【2】 whether the whole thing could still 【3】 (call) off.Theresa May, the first Conservative Prime Minister with the job of taking the 人们利用化学反应，分别都有不同的目的．工业上将铜矿石(例如孔雀石)煅烧后，再用C或CO还原，其目的是什么？冬天，人们将火炉里的木炭点燃后燃烧的目的是什么？在汽车的发动机里，让汽油和空气里的氧气反应，其目的又是什么？