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The planet Mars is the closest and most similar planet to Earth． It is very（1） 　　to scientists． For example， Mars has seasons with（2） 　　weather， but other planets have the same temperatures all year round． Was there（3） 　　on Mars？

To find out， scientists need（4） 　　if Mars ever had water． In 2004， two robot explores （探测器）， or 'rovers'， called Spirit and Opportunity were sent to look for（5） 　　of water． These rovers can drive over rocks（6） 　　all kind of rough ground． They can also use cameras and send photos（7） 　　to Earth． First， the two rovers found chemicals and patterns （图纹） in the rocks that were probably made by water． Then， they moved to another area and（8） 　　other rocks which may have been created by water． Now scientists think there was probably water on the planet long ago． Today （9） 　　are still not sure if there was life on the mars． They（10） 　　need more information to decide． The discoveries of the two rovers answered some old questions， but they also brought up many new ones．