对于下面所列举的几种气体，比空气轻的气体有（） A.CH4 B.NH3 C.H2 D

海关对于进口列入自动许可证管理的化肥溢短装数量在货物总量正负5%以内予以免证验放。

肠易激综合征（）。

A.高渗性腹泻

B.吸收障碍性腹泻

C.分泌性腹泻

D.运动性腹泻

E.药源性腹泻

吉尔福特提出的智力理论是【】

A．单因素论

B．二因素论

C．群因素论

D．三维结构理论

患者女性，12岁，因“左下后牙咬合痛1个月”来诊。口腔检查：左下5畸形中央尖穿髓，探诊（-），叩痛（+），松动（-），牙龈正常。X线片：左下5牙周膜增宽，硬骨板不连续，牙根未完全发育。

根尖诱导成形术主要依赖的干细胞为（）

A.根尖部残留的生活牙髓

B.根尖部的牙 * *

C.根尖周组织的上皮根鞘

D.根尖周成骨细胞

E.根尖周骨细胞

F.根尖周牙周膜细胞

It is hard to predict how science is going to turn out, and if it is really good science it is impossible to predict. If the things to be found are actually new, they are by definition unknown in advance. You cannot make choices in this matter. (46)You either have science or you don’t, and if you have it you are obliged to accept the surprising and disturbing pieces of information, along with the neat and promptly useful bits.

The only solid piece of scientific troth about which I feel totally confident is that we are profoundly ignorant about nature. Indeed, I regard this as the major discovery of the past hundred years of biology. It is, in its way, an illuminating piece of news. (47)It would have amazed the brightest minds of the 18th century Enlightenment to be told by any of us how little we know and how bewildering the way ahead seems. (48)It is this sudden confrontation with the depth and scope of ignorance that represents the most significant contribution of the 20th century science to the human intellect. In earlier times, we either pretended to understand how things worked or ignored the problem, or simply made up stories to fill the gaps. Now that we have begun exploring in earnest, we are getting glimpses of how huge the questions are, and how far from being answered. Because of this, we are depressed. (49)It is not so bad being ignorant if you are totally ignorant; the hard thing is knowing in some detail the reality of ignorance, the worst spots and here and there the not-so-bad sports, but not true light at the end of the tunnel nor even any tunnels that can yet be trusted.

But we are making a beginning and there ought to be some satisfaction. There are probably no questions we can think up that can’t be answered, sooner or later, including even the matter of consciousness. (50)To be sure, there may well be questions we can’t think up, ever, and therefore limits to the reach of human intellect, but that is another matter. Within our limits, we should be able to work our way through to all our answers if we keep at it long enough, and pay attention.

(50)To be sure, there may well be questions we can’t think up, ever, and therefore limits to the reach of human intellect, but that is another matter.