Scientist are not sure about the of water on the Mars.A. occupationB. existenceC. demandD

问题补充：

Scientist are not sure about the of water on the Mars.

A. occupation

B. existence

C. demand

D. treasure

答案：

A. occupation

(答案→)B. existence

C. demand

D. treasure

解析：词义辨析。occupation 职业，占有；existence存在，生存；demand要求，需要；treasure财富，财宝。句意：关于火星上水的存在科学家们不确定。选B。