填入下面一段文字横线处的语句，最恰当的一句是（    ）

职责的转变与业务量的增加使得对消防员的要求也越来越高，                    。新兵从一个地方青年到一个合格的消防战斗员，通过训练和实战需要半年到一年左右的时间。除了理论知识的学习，体能的训练，心理素质也是极为重要的一项课程。后期实战也会让新人真正深入到各种突发灾害中，让其心理素质和胆量在训练和实战中得到强化。

      The day is like any other day in his life. Tom walks past the shop on the street corner. He stops to look at the front row of shoes, and he feels happy to see that the pair of shoes he wants very much is still there. Looking down at his old shoes, he feels sorry for himself. He really wants to have them for his birthday.
       He sadly walks away and thinks how to tell his mother about it. He knows very well she has little money. He decides not to go home at once , as he looks sad and his mother will notice(注意) it. So he goes to the park and sits on the grass. There he sees a boy moving a wheelchair（轮椅）with his hands . Tom looks at him and is surprised to see that the boy has no feet. He looks at his own feet. “It's much better to be without shoes than without feet”, he thinks. There is no reason or him to feel so sorry and sad. He goes away and smiles, thinking he is happier.

我国人口分布的基本特点是    （    ）