能造成细胞膜对Na通透性突然增加的临界膜电位为（） A.动作电位 B.阈电位 C.局

Light travels at a speed which is about a million times faster than the speed of sound. You can get some idea of this difference by watching the start of a race. If you stand some distance(距离) away from the starter, you can see smoke from his gun before the sound reaches your ears.

This great speed of light produces some strange facts. Sunlight(太阳光) takes about 8 minutes to reach us. If you look at the light of the moon tonight, remember that the light rays left the moon 1.3 seconds before they reached you. The nearest star is so far away that the light that you can see from it tonight started to travel towards you four years ago at a speed of nearly 2 million km. per minute. In some cases, the light from one of tonight’s stars had started on its journey to you before you were born.

Thus, if we want to be honest, we can’t say, “The stars are shining tonight.” We have to say instead, “The stars look pretty. They were shining four years ago, but their light has only just reached the earth.”

小题1:Light speed is ______ sound speed.

A．as fast as

B．a million times slower than

C．about millions of times faster than

D．about a million times faster than小题2: If you stand 200 meters away from a man who is firing a gun to start a race, you will find out that ______.

A．you can hear the sound before you see the smoke

B．the sound does not travel as fast as light

C．the sound will reach you before the man fires

D．sound travels about a million times faster than light小题3:Sunlight obviously(显然的) ______ than the light of the moon.

A．has to travel a greater distance

B．moves less quickly

C．travels much more quickly

D．is less powerful小题4: The scientific way of saying "The stars are shining tonight" should be ______.

A．the stars have been shining all the time

B．the stars seen tonight will shine four years later

C．the stars were shining long ago but seen tonight

D．the starlight seen today could be seen four years ago

人为坑洞地区地表建筑物变形及地面变形与下列( )无密切关系。

A．(A) 采空区的开采历史

B．(B) 顶板管理方法

C．(C) 开采工作推进方向和速度

D．(D) 开采矿床的种类

混合氯酸钾和红磷可制成运动会上用的发令响炮，它一受撞击便会发出响声，并产生白烟．其化学方程式为______．

近代警察是适应封建主义制度需要而建立起来的专门执行警察职能的机胸和官吏。 ( )

临床资料：男，48岁，常规体检。

超声综合描述：胰头、胰体表面光滑，回声均匀；胰尾可见1．6cm×1．6cm无回声区，包膜光滑，内透声清亮。

超声提示（）

A.肠系膜囊肿

B.胰尾胰岛细胞瘤

C.胰尾真性囊肿

D.胰尾假性囊肿