与图中的巴尔喀什湖，以湖水东部咸西部淡著称于世。图中沙漠的成因是（    ）

若函数f（x）=sinωx+$\sqrt{3}$cosωx，x∈R，又f（a）=2，f（β）=0，|α﹣β|的最小值等于$\frac{5\mathrm{\pi }}{4}$，则正数ω的值为（　　）

    More people like Living in a city now, especially young people who like new and modern things. Most people think it is much ____ （容易） to find work in a city . They think there are a lot of ____ (有乐趣的) things to do and places to see in the city . There are also many ____ (选择) of public transport. When they feel tired, they can eat in good restaurants, visit museums, go to cinemas and go to parks.

    ____ （然而）, in my opinion, living in the city will ____ (花费) more . What's more, the ____ (人口) of the city is getting bigger and bigger.  so it's a ____（遗憾） that the city is always ____ （拥挤的） noisy and dirty. And It is very difficult to find a good place where people can enjoy ____（和平） and fresh air. So We should ____ （改善） the serious situation.

命题“任意多面体的面至少有一个是三角形或四边形或五边形”的结论的否定是____．