10.5 放狗

fuckoffand

霁月月月 发表于 2018-10-5 17:13
x+y=5k1+1 y+z=5k2+2 x+z=5k3+3 三个式子相加就是2(x+y+z)=5(k1+k2+k3)+6 两边再除以二

如果兩邊／2的話那麼就變成x+y+z=5/2 (...) +3, 看似就不被5除了。。。

霁月月月

fuckoffand 发表于 2018-10-5 17:42
如果兩邊／2的話那麼就變成x+y+z=5/2 (...) +3, 看似就不被5除了。。。

括号内的一定是偶数，因为在你没除以二时左边是偶数，右边只能是偶数+偶数，所以除以2以后5可以保留，一定是5乘以一个整数再+3

vickychi0913

帮你补充一下哈，图形的DS题 1) x=30, 2)两个圆弧都是以小正方形边长为半径的1/4圆
答案是B，只有第二个已知，就可以求出来阴影面积的fraction，不需要知道x的值

Sibyllam

vickychi0913 发表于 2018-10-5 18:18
帮你补充一下哈，图形的DS题 1) x=30, 2)两个圆弧都是以小正方形边长为半径的1/4圆
答案是B，只有第二个已 ...

THX!~ 我补充到主楼里去了

开心尾气

感谢

billyisfragile!

关于脊椎动物的演化，第一段说很多脊椎动物的化石发现在海洋里，所以有学者觉得脊椎动物是从海里演化的（关于这个学者有道题），但有种O化石被发现在淡水或混合环境里，且有淡水生物的特征，所以也可说明脊椎动物在淡水里演化。
第二段说淡水里食物什么的相比海水而言都比较匮乏（这一段有道高亮题，问作者说提到这点是想说明什么），但淡水里捕食者（还是竞争？）更少，所以利于脊椎生物演化。
第三段好像说的是一个洄游现象，有些脊椎生物会在更安全的淡水产卵然后游回海水里，后来就演化成了今天三文鱼之类的品种。

是原文吗？

The fossil record of very early vertebrates

Small fragments of dermal bone that occur in marine deposits from the end of the Cambrian and from the early Ordovician periods are generally regarded as the oldest vertebrate fossils (Repetski 1978). The geological periods and examples of their fauna are shown in Figure 2. The earliest traces of vertebrates are sporadic and poorly characterized, but Middle Ordovician vertebrates are well known and abundant in certain restricted localities, notably the Harding sandstone formation of Colorado. The Harding sandstone vertebrates were jawless fishes with bony shields (ostracoderms) of the genera Astraspis and Eriptyckius. Until recently, they were believed to have inhabited shallow marine environments (Darby 1982) or per- haps estuaries with variable salinity (Spjeldanaes 1979).

P2. 然而，很多年前，fresh water 环境相比现在 sterile(这里提到了 coastal sea 资源更丰富 什么的)，脊椎动物不可能一开始就生活在淡水里，更像是从海水逐渐跑到淡水里去的。淡 水产卵，长大了游回大海，这样既避免了海水里天敌的侵扰，获得了淡水情况下稳定的生

Freshwater rivers are usually less productive than estuaries or coastal seas. During the early Paleozoic, when there were no multicellular freshwater or terrestrial plants or animals, the rivers were probably more sterile than they are today. Consequently, feeding would not favor movement from estuaries into fresh water.

Freshwater rivers, however, would have held a decided advantage over Paleozoic estuaries and coastal seas as safe havens for reproduction and early development. There were no river predators or competitors, and rivers are more stable than estuaries in environmental variables important to development such as salinity, sedimentation, and oxygen levels.

P3. 众所周知淡水的营养比海水差，过去的淡水比现在的好些，可是也比海水差。However， pre 脊椎鱼选择到淡水区和混水区除了看中了这里养分也还有一些，最重要是因为淡水区没 有食物，所以没有那么多天敌(这里考到了，说为什么选择淡水)。但是也因为淡水养分少， 所以很多鱼都是选择在淡水繁殖和养育后代，成年后再回到海水中。这也就是现在还有的回游特性，比如 salmon

Freshwater protovertebrates would have grown slowly and had limited reproductive potential, unless they migrated to nearby estuaries and coastal marine habitats to feed after they had grown big enough to compete successfully with marine species. A strictly freshwater protovertebrate makes little sense ecologically, but anadromy, with breeding occurring in fresh water and juveniles feeding and growing rapidly in estuaries and the sea, would have been a reasonable lifestyle during the early Paleozoic, as it is today for lampreys, sturgeon, striped bass, and salmon.

Sibyllam

bzy! 发表于 2018-10-5 21:56
是原文吗？

The fossil record of very early vertebrates

不完全重合，后两段应该是一样的，第一段有差别

billyisfragile!

Sibyllam 发表于 2018-10-5 22:08
不完全重合，后两段应该是一样的，第一段有差别

是这段改写吗？

Did the vertebrates originate in the sea or in fresh water?

Perhaps the single most important and most often debated question concerning the origin of vertebrates is whether it occurred in the sea or in fresh water. This question has more significant implications than the simple salt content of the habitat. More than 500 million years ago, at the presumed time of vertebrate origins, freshwater rivers and lakes are believed to have lacked multicellular animals, whereas the seas already possessed a rich and diverse fauna. If the vertebrates originated in the sea, their body plan would have evolved in the contexts of acute predation, competition, and varied and abundant food supplies. In fresh water, on the other hand, there would have been no predators or competitors, and the dietary options would have been limited to algae and other unicellular organisms. One cannot imagine two more divergent stages for the beginnings of the vertebrate evolutionary play.

The living protochordate relatives of the vertebrates all live in the sea, and there can be little doubt that the vertebrate line is ultimately derived from marine ancestors. However, because most living and fossil groups of fishes include freshwater branches, it is reasonable to pro-pose that a common ancestor of all vertebrates might have moved from the sea to fresh water.

The debate over freshwater or marine origins has historically included arguments from two sources: paleontological data that tell us the apparent habitat of the earliest fossilized vertebrates and the physiology of water and salt balance in living fishes, especially primitive ones such as the jawless hagfish.

cindy750宝宝

verapancake 发表于 2018-10-5 15:55
感谢狗狗！
请问 已知x+y被5除余1，y+z被5除余2，x+z被5除余3，问x+y+z被5除余几 这道题答案是3吗 ...

我算的也是3，明天考试，冲鸭！！！！！！

fuckoffand

霁月月月 发表于 2018-10-5 18:13
括号内的一定是偶数，因为在你没除以二时左边是偶数，右边只能是偶数+偶数，所以除以2以后5可以保留，一定 ...

讚！