已知A，B是双曲线$\frac{x^2}{a^2}-\frac{y^2}{b^2}=1(a>0,b>0)$的两个顶点，P为双曲线上（除顶点外）的一点，若直线PA，PB的斜率乘积为$\frac{1}{2}$，则双曲线的离心率e＝(  )

①尊重规律是实践活动取得成功的前提条件

②客观实在性是物质的根本属性

③积极创造条件利用规律才能实现人与自然和谐相处

④发挥主观能动性与尊重客观规律总是统一的

先通读下面的短文，然后根据短文内容，在空格内填入一个最适当的词，所填单词必须在答卷标有题号的横线。每空只能填一字

What is a hurricane?(飓风)

    You may already know that hurricanes are storms that can cause devastating(毁灭性的) waves, wind, and rain. They happen during “Hurricane Season,'' from June 1st until November 30th in the Atlantic Ocean and from May 15th until November 30th in the Pacific Ocean.

Categories(类别)of Hurricanes

    There are five categories of hurricanes, which are based on wind speeds. The categories help people know how much damage(危害) a hurricane may cause because the greater the wind speed, the more dangerous the storm. For example, a Category 5 hurricane has winds over 155 miles per hour, which are strong enough to break the buildings along the seaside completely.

Hurricane Dangers

    When a hurricane happens together with heavy rainfall（降雨）, there can be a devastating flood. The centre of a hurricane is called the eye. While most of a hurricane has dangerously strong winds, the eye in fact is a calm area in the storm. When the eye of a hurricane passes over land, people might think that it's over, but before long the wind and rain increase(增长) again as the second part of the hurricane moves through.

Hurricane Safety Tips

    There is no way to stop a hurricane or make it change direction, so if you ever find yourself in the path of a hurricane, be sure to stay inside during the storm. You could be seriously injured(受伤) if you go outside.

一些青少年崇拜影视剧中的吸烟镜头，认为吸烟时髦、潇洒，有个性，于是追求、模仿。对于青少年吸烟的相关认识不正确的是（    ）