话不多说先来做道题：

Outflow channels are probably relics of catastrophic flooding on Mars long ago. They appear only in equatorial regions and generally do not form extensive interconnected networks. Instead, they are probably the paths taken by huge volumes of water draining from the southern highlands into the northern plains. The onrushing water arising from these flash floods likely also formed the odd teardrop-shaped “islands” (resembling the miniature versions seen in the wet sand of our beaches at low tide) that have been found on the plains close to the ends of the outflow channels. Judging from the width and depth of the channels, the flow rates must have been truly enormous—perhaps as much as a hundred times greater than the 105 tons per second carried by the great Amazon river. Flooding shaped the outflow channels approximately 3 billion years ago, about the same times as the northern volcanic plains formed.

According to paragraph 2, all of the following are true of the outflow channels on Mars EXCEPT:

A. They formed at around the same time that volcanic activity was occurring on the northern plains.

B. They are found only on certain parts of the Martian surface.

C. They sometimes empty onto what appear to have once been the wet sands of tidal beaches.

D. They are thought to have carried water northward from the equatorial regions.

-----TPO8-3

Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury. In English, Mars carries a name of the Roman god of war, and is often referred to as the "Red Planet" because the reddish iron oxide prevalent on its surface gives it a reddish appearance that is distinctive among the astronomical bodies visible to the naked eye. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth.   

                        ----维基百科

火星（Mars）

的名字源于罗马神话中的国土与战争之神玛尔斯（Mars）。它是太阳系中由内往外数的第四颗行星（planet），属于类地行星（Terrestrial）。

在此对太阳系八大行星做个小梳理，由内到外排序分别为：

1.水星（Mercury）

2.金星(Venus)

3.地球(Earth)

4.火星(Mars)

5.木星(Jupiter)

6.土星(Saturn)

7.天王星(Uranus)

8.海王星(Neptune)

Ps：冥王星（Pluto）在2006年召开的国际天文学联合会第26届大会上被从太阳系九大行星除名，降为矮行星，因为其不符合作为行星的第三个条件：

一、以近似圆形的轨道围绕恒星运转。

二、质量足够大，能依靠自身引力使天体呈圆球状。

三、能逐渐清除其轨道附近的天体。

太阳系中的行星被分为两大类，分别为类地行星(Terrestrial)和类木行星(Jovian)

The planets in our solar system fall into two groups: the terrestrial (Earth-like) planets (Mercury, Venus, Earth, and Mars) and the Jovian (Jupiter-like) planets (Jupiter, Saturn, Uranus, and Neptune).            

                      -----TPO16-3

Terrestrial：Mercury、Venus、Earth、Mars

features：

-made of rocky material

-surfaces are solid

-don’t have rings

-very few moons

-relatively small

Jovian：Jupiter、Saturn、 Uranus、Neptune

features：

-multiple moons

-no solid surface

-support ring system

-immense in size

好了，科普完太阳系的行星及分类，我们继续来讲今天的小可爱---火星。

火星和地球一样拥有多样的地形，有高山、平原和峡谷，火星基本上是沙漠行星，地表沙丘、砾石遍布，常常伴有沙尘暴，其风速每秒达到180多米, 而我们通常所说的12级台风，风速才达到每秒32.6米，所以火星上沙尘暴强度可想而知，而火星沙尘暴的持续时间也很长，一旦刮起来可持续三个多月，从地球上望去，就像一个暗红色的灯笼。

火星的南北半球的地形有着强烈的对比。火星的南半球，有着与月球上相似的曲型的环状高地；相反的，它的北半球大多由低平的平原组成，两者之间以明显的斜坡分隔。

火星表面的无水、干涸“河道”,有流水冲刷现象。其类型主要有径流河道(runoff channels)和溢流河床(outflow channels),在北纬30°到南纬40°之间特别普遍,是显著的地形特征。许多河道有较大的波形弯曲,有的河道呈辫状、网状、树枝状,大河火星河道及其分岔现象道向河口逐渐加宽。

径流河道多存在于火星南方高地，河道呈网状，并互相联系，形成大的河道网。地质学家认为这些河道是远古的已干涸的河流的河床。

溢流河道存在于火星赤道，与径流河道不同的是，溢流河道不形成河道网，地质学家认为它是远古大水从高地到北方平原的冲刷痕迹。这种冲刷还形成了泪状的“岛屿”，就像低潮时沙滩上的浅坑。

有了背景知识助攻，大家知道该选哪个选项了吧！