题目

For centuries, humans have wondered whether there is life on Mars. Scientists have asked why Mars is losing its atmosphere. Last week, the question was answered with a song. “The answer is blowing in the wind,” said Michael Meyer, taking a line from a Bob Dylan song. Meyer is the lead scientist for NASA’s Mars Exploration Program. It turns out that solar winds from the sun are slowly blowing away Mars’ atmosphere.Today, Mars has a thin atmosphere. It is cold and dry, with a desert-like environment. Jakosky says it used to be much more different. “When we look at ancient Mars, we see 图是植物幼根的根尖模式图，据图回答问题（1）根尖的主要吸水部位是________，当外界土壤溶液的浓度________（填大于或小于）细胞液浓度时，细胞吸水，通过________运送到植物体各处． （2）细胞较大，形状不规则，排列不整齐的部位是________。 （3）________细胞数量的增加和________细胞体积的增大，使根不断地向地下延伸。