煤是重要的能源，也是化工生产的重要原料．

（1）煤燃烧产生的废气直接排放到空气中，可能导致的环境污染问题是 ____．

（2）下图是对煤燃烧产生的废气进行常温脱硫处理的流程示意图．

①废气脱硫过程中，主要反应的化学方程式为 ____ ____

②在煤中直接添加一种物质，可有效减少煤燃烧产生的SO₂，该物质是 ____

③石膏在工业生产中的用途是 ____（写出一种用途即可）．

（3）煤经过 ____（填加工方法）可以得到炉煤气、煤焦油和焦炭．煤焦油经过 ____（填加工方法）可得到芳香族化合物．煤也可以用氢化法转化成燃油，氢化法的本质是 ____

下面的结论正确的是(  )

有50件产品编号从1到50,现在从中抽取5件检验,用系统抽样确定所抽取的编号为(    )

The long trunk of an elephant is a wonderful example of skill. The neck of four-footed animals is usually long, to have them reach their food without difficulty, but the elephant has a short neck, to make him more easily support the weight of his huge head and heavy teeth.   His long trunk lets him get his food easily.

The trunk of an elephant is to him what the neck is to other animals. It is also a nose to him, for at the end of it there is a empty place like a cup, and in the bottom of the cup are two holes, and the animal smells and breathes through them. It is an arm and a hand too, so that it has been said that the elephant carries his nose in his hand, and it might also have been said that he breathes by his hand.

 At the end of the trunk, there is a strange part, about five inches long, which forms a finger. With this finger the animal can pick up the smallest piece of money from the ground, and he has been taught to make marks like letters with a pen.

The trunk of a full-grown elephant is about eight feet long. The elephant has such great strength that he can knock down a man with it.