C．It has some valleys.

　　D．It is usually dry.

　　D　[细节理解题。根据第一段中的"Racetrack Playa，the waterless lakebed"和第四段中的"No river flows into the playa"可知，赛马场盐湖经常是干涸的。]

　　2．What was the park's attitude to using GPS in the lakebed's stones?

　　A．It doubted the method.

　　B．It was against doing so.

　　C．It felt it was worth a try.

　　D．It thought it was useless.

　　B　[推理判断题。根据第三段中的"They were not allowed to move or change anything of the existing playa stones"可知，死亡谷国家公园不允许科学家在赛马场盐湖的石头上使用全球定位系统。]

　　3．Why do the stones "sail" according to the Norrises?

　　A．They are moved by big floods.

　　B．They move just because of strong winds.

　　C．They are mainly pushed by wind­driven ice.

　　D．They move very slowly on smooth ice sheets.

　　C　[细节理解题。根据第四段中的"Driven by light winds，the sheets push up against rocks"可知，两位科学家认为，石头周围形成的冰在风的作用下使得石头移动。]

　　4．What does the underlined word "episodic" in the last paragraph probably mean?

　　A．Amazingly big.

　　B．Extremely slow.

　　C．Happening sometimes.

　　D．Going on without stopping.

C　[词义猜测题。由最后一段可知，能够让石头移动的条件非常特殊，很少出现，所以可推断episodic应该是"偶尔发生"的意思。]