如图所示，圆锥体重为G，悬浮在水中时受到水对它向上的压力为F1，向下的压力为F2

男性，35岁。重症肺炎并发ARDS，行气管内插管机械通气后出现持续性低血压，其可能性较大的原因是（）

A.发生消化道大出血

B.发生心力衰竭

C.发生深静脉血栓

D.发生肺梗死

E.正压通气使胸内压增高，心排血量减少，血压下降

下列关于浓硫酸的说法中不正确的是

A.蔗糖中加入浓H₂SO₄后出现发黑现象是因为浓硫酸具有脱水性

B.向25 mL 18 mol·L^-1浓硫酸中加入足量铜片，被还原的H₂SO₄的物质的量等于0.225 mol

C.常温下，冷的浓硫酸可以用铁或铝的容器贮存，是因为铁或铝发生了“钝化”

D.如图，小试管中有3mL水，U型管内有少量的水。沿小试管壁小心地注入3mL浓硫酸，静置片刻后，U型管中的液面是左低右高

工程资料的内容必须（）。

A.真实

B.及时

C.保持同步

D.准确

E.与工程实际相符合

腹腔镜在术中造气腹时，下列哪一项是错误的

A．有两次突破感

B．注射器内的盐水迅速流入腹腔

C．Palmer抽吸试验阳性

D．肥胖病人的腹壁突破感明显

E．流量计在4L/min时不应超出1．73kPa

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 truth 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 spots, but no 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.