现在网络聊天成为交友的一种新时尚，有的人通过网络聊天开阔了视野，增进了友谊。也有不少人上当受骗，在人生中留下惨痛的教训。因此，在网络交往中，我们应该（   ）

新华网悉尼2014年12月16日电 澳大利亚警察16日凌晨2时10分冲入悉尼马丁广场发生人质劫持事件的咖啡馆，与劫持者交火，造成3人死亡、4人受伤。12月16日，塔利班武装分子袭击了巴基斯坦西北部地区一个军队管理学校，数百名学生和教师被劫为人质。最新消息显示，事件已造成130人死亡，另有120余人受伤，遇难者中有多名孩子。这些事例表明威胁和破坏世界和平的因素是（  ）

人们常用“冰山一角”来形容事物显露出来的仅仅是其很小的一部分，更多的还隐藏在表面现象之下．事实上，冰山浮在海水中的确只露“一角”，那么这露出的“一角”到底占冰山大小的多少呢？请你用物理知识通过计算来说明．

（已知ρ_海水=1.03×10³kg/m³，ρ_冰=0.9×10³kg/m³）

可持续发展是我国的必然选择，是因为（   ）
①庞大的人口压力
②资源短缺令人担忧
③经济发展速度较慢，底子薄
④深刻的环境危机

完形填空

先通读下面的短文，掌握其大意，然后在每小题所给的A、B、C、D四个选项中，选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。

Few people like changing their habits, good or bad. Whether it is smoking, drinking or over-eating, they 1“enjoying”them to the end.

On every packet of cigarettes(香烟), people are warned against the2of smoking: “Warning: Cigarette Smoking Is Dangerous to Your Health”.3, millions of them start smoking or go on smoking. Why?

Facts show that families and surroundings(环境) play a very important part in 4 smokers. All those smokers come from smoking families or have smoking5 or relatives. Films and TV plays also play a part. People6their “heroes" on TV drinking alcohol(酒) or smoking cigarettes. “Heroes” seem to fear7, neither killing themselves nor killing others with alcohol and cigarettes. If they are not afraid of the harm of smoking and drinking,8should common people be afraid?

The simple warning on the cigarette packet does not influence smokers' habits. Even 9warnings, like showing pictures of smokers who have died of cancer, don't seem to work.  

Knowing and believing seem to be two10 things. If smoking is really as harmful as doctors say, it is time for smokers to think about it and try to give it up!