纳税人应当保存好已开具的发票存根联和发票登记簿，保存期满后可自行销毁。 ( )

某校食堂中餐食谱如下：主食：大米饭配菜：红烧排骨，煎鸡蛋，炸鸡腿，豆腐汤，炒猪肝主食和配菜中主要含维生素、 _________ 、 _________ 、 _________ 、无机盐、水等营养素，考虑到各种营养成分的均衡搭配，应该增加的配菜是 _________ ．

What makes it rain? Rain falls from clouds for the same reason anything falls to Earth. The Earth's gravity pulls it. But every cloud is made of water droplets or ice crystal(冰晶). Why doesn't rain or snow fall constantly from all clouds? The droplets or ice crystals in clouds are extremely small. The effect of gravity on them is slight. Air currents move and lift droplets so that the net downward amount of water is zero, even though the droplets are moving constantly.

It can be seen that droplets and ice crystals behave somewhat like dust in the air in a beam of sunlight. To the casual observer, dust seems to act in a totally random fashion, moving about

without fixed direction. But in fact dust particles（分子） are much larger than water droplets and they finally fall. The average size of a cloud droplet is only 0.0004 inch in diameter（直径）. It is so small that it would take sixteen hours to fall half a mile in perfectly still air, and it doesn't fall out of moving air at all. Only when the droplet grows to a diameter of 0.008 inch or larger can it fall from the cloud. The average raindrop contains a million times as much water as a tiny cloud droplet. The growth of a cloud droplet to a size larger enough to fall out is the cause of rain and other forms of precipitation. This important growth process is called "coalescence".

小题1: Ice crystals do NOT immediately fall to Earth because           .

A．they are kept up by air currents

B．most of them change into steam

C．they combine with other chemicals in the atmosphere

D．their electrical charges draw them away from the earth小题2: The underlined word "random" in line 10 most probably means            .

A．unpredictable

B．strict

C．independent

D．abnormal小题3:What can be inferred about drops of water larger than 0.008 inch in diameter?

A．They never occur.

B．They are not affected by the force of gravity.

C．In moving air they would fall to earth.

D．In still air they fall a speed of thirty-two miles per hour.小题4: How much bigger is the rain drop than a loud droplet?

A．200 times bigger

B．1,000 times bigger

C．100,000 times bigger

D．1,000,000 times bigger

醛酮与羧酸及其衍生物的缩合包括（）

A.珀金反应

B.诺文葛尔-多布纳缩合

C.达曾斯缩合

D.克莱森缩合

严重的烧伤可导致身体失去（）。

A、大量红细胞

B、大量白细胞

C、大量血浆

分泌胰岛素的细胞是（）。

A.贝塔细胞 

B.P细胞 

C.阿拉法细胞 

D.β细胞 

E.导管细胞