小明和妈妈用手机通电话，下列说法正确的是（　　）

已知a+b=2，a﹣b=3，则a²﹣b²=____ .

已知曲线C₁的参数方程为 $\{\begin{array}{l}x=-1+t\cos \alpha \\ y=3+t\sin \alpha \end{array}$ （t为参数，0≤α＜π），以坐标原点O为极点，x轴正半轴为极轴建立极坐标系，曲线C₂的极坐标方程为ρ=2 $\sqrt{2}$ sin（θ+ $\frac{\pi }{4}$ ）．

（Ⅰ）若极坐标为 $\left(\sqrt{2},\frac{\pi }{4}\right)$ 的点A在曲线C₁上，求曲线C₁与曲线C₂的交点坐标；

（Ⅱ）若点P的坐标为（﹣1，3），且曲线C₁与曲线C₂交于B，D两点，求|PB|•|PD|．

根据短文大意选择单词并用其正确形式填入空白处,使补全后的短文意思通顺,语法正确,结构完整. 

    Trees are useful in three important____  .The most important way is that they  provide man with food , wood and other products. Trees provide food not only for man, but also for animals.____trees, many animals could not live on the earth. It's not ____ for man to live on the earth, either.
    The second important way is that trees give us shade(树荫). On a hot summer day, people are eager to have a rest under the shade of a tree after____a long way. You can imagine how important the shade of a tree is to man and animals.
    The third important way is that trees help to____ droughts and flood. However, in many parts of the world, man hasn't realized it. He has cut trees down in large numbers. In the end, he finds that he has lost the best friends he had.

下列关于气温和降水分布规律的说法，正确的是（   ）