男性，30岁，外伤性血胸已2周，出现发热、胸痛等症状，经多次胸穿抽液后，症状无明显改

指出下列句子所使用的说明方法。

①石拱桥的桥洞成弧形，就像虹。（　　 ）

②永定河发水时，来势很猛，以前两岸河堤常被冲毁，但是这座桥却从没出过事，足见它的坚固。（　　 ）

③唐朝的张嘉贞说它“制造奇特，人不知其所以为”。（　　 ）

④宫城呈长方形，占地72万平方米，有大小宫殿七十多座、房屋九千多间。（　　 ）

短文填空。

     Tom and Fred are t    l      about the year 2050.

     "What will the world be like in the year 2050?" asks Tom.

     "I don't know,"says Fred.  "What do you t   2    ?"

     "Well, no one knows. But it is interesting to guess," says Tom.  "In the year 2050 everyone will

c   3   a pocket computer. If we have problems, the computers will give us a   4     . And we can talk to

our friends all over the world. P 5      we will work only two or three days a week. We can f   6    to

the moon by spaceship and spend v   7    there. "

     "I'm very glad to h   8    that. I h  9    to fly to the moon, and I also hope to   10    in the sea," says

Fred. "Won't that be very interesting? Just like a fish. "

Sorry,there isn't any         .[ ]

A.eggs

B.food

C.melons

特雷诺指数考虑的是( )。

A．全部风险

B．不可控制风险

C．市场风险

D．股票市场风险

家猫体色由X染色体上一对等位基因B、b控制，只含基因B的个体为黑猫，只含基因b的个体为黄猫，其他个体为玳瑁猫。下列说法正确的是（）

A.玳瑁猫互交的后代中有25%的雄性黄猫

B.玳瑁猫与黄猫杂交后代中玳瑁猫占50%

C.为持续高效地繁育玳瑁猫，应逐代淘汰其他体色的猫

D.只有用黑猫和黄猫杂交，才能获得最大比例的玳瑁猫