盆栽的植物，一般不宜经常放在卧室内过夜，这是因为（    ）

B

    Handshaking is a kind of silent language. It is the common politeness on most social occasions as an expression of etiquette(礼仪) and greeting when people meet or say goodbye to each other. Besides, handshaking is also a way to express congratulations, thanks and encouragement to others.

    Who should offer his hand first? There are some rules you should follow. Generally speaking, the elder, the senior(长辈), the teacher, the female, the married, the leader should reach out their hands first. If you have to shake hands with more than one person, you should shake hands in turn with the senior and leader to the junior and low—grade, from the nearest to the furthest. Specially, when the host meets the guest, the host should shake hands first to show his welcome; however, when they say goodbye with each other, it is the guest who should offer this hand first.

    Then how to shake hands with others? It is not right to shake hands too long or too short, three to five seconds is the best, not go ahead to 30 seconds at most. There are also some things that are uncomfortable when shaking hands. You can't shake hands carelessly or with left hand. Before you shake hands, you should take off your hat, gloves, sunglasses first. You had better not refuse to shake hands with others or shake hands while having your other hand in your pocket.

在生产和生活中，人们常把密度作为所选材料的主要考虑因素，下面属于主要从密度的角度考虑选材的是（　　）

阅读下面的短文，补写出横线处的内容。要求紧扣议论主题，语意连贯，表达明确。每句不超12个字。

    雾霾天气来来回回，深受其害的人不禁要问，____？环保部副部长吴晓青的答复是：“欧美发达国家耗费了30至50年才基本解决大气污染问题，我们要做好打持久战的思想准备。”

    雾霾治理工作有艰巨性、复杂性，以此为理由，得出三五十年的结论，未免要让两代人感到绝望。据钟南山透露，pm2．5的危害甚至超过了“非典”。北京近十年来肺癌患者增加了六成，如果雾霾天气再肆虐三五十年，中国人的健康又将受到怎样的伤害？

    欧美发达国家用了三五十年，但是这不意味着中国必须重走这条路。____，中国应该回避欧美发达国家当初的弯道和误区。与其空谈三五十年后会怎样，不如____ ，这才能让人民看到希望。