超声波及其应用

人能够听到声音的频率范围从20 Hz到20 000 Hz。低于20 Hz的声音叫次声波，高于20 000 Hz的声音叫超声波。

超声波具有许多奇异特性：空化效应——超声波能在水中产生气泡，气泡爆破时释放出高能量，产生强冲击力的微波水柱，这不断冲击物体的表面，使物体表面及缝隙中的污垢迅速剥落，从而达到净化物体表面的目的。传播特性——它的波长短，在均匀介质中能够定向直线传播，根据这一特性可以进行超声波探伤、测厚、测距、医学诊断等。

把下列与燕子有关的诗句补充完整，并背诵。

①泥融飞____，沙暖睡鸳鸯。（杜甫《绝句》）

②几处早莺争暖树，谁家____啄春泥。（白居易《钱塘湖春行》）

③细雨鱼儿出，微风____斜。（杜甫《水槛潜心二首》）

④无可奈何花落去，似曾相识____归来。（宴殊《浣溪纱》）

根据图象直接写出使kx+b＜$\frac{6}{x}$成立的x的取值范围

     Mr. Green lives in a big city with his wife and two children. One morning Mr. Green takes his new car and washes it when a friend comes. The friend stops and looks at the new car for a minute. Then he asks, "That's a new car. Is it yours? "
"Sometimes." Mr. Green answers.
   The friend is surprised (惊奇). "Sometimes? " he says. "What do you mean?" Mr. Green answers slowly, "Well, when there is a party in town, my daughter Jean drives it. When there is a football, it's my son Jim's turn. When I washes it and it looks very nice and clean, my wife Linda uses it. And when it needs cleaning. It's mine. Choose the correct answer.

下面是温带草原生态系统示意图，请认真观察如图后分析并回答下列问题：