Scientist are not sure about the of water on the Mars.
A. occupation
B. existence
C. demand
D. treasure
网友回答
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。