问题
选择题
Some solid evidence proves that water really exists on Mars, but unfortunately, there is still no of life.
A．mark
B．sign
C．symbol
D．signal
答案
答案：B
题目分析：考查名词。A标记；B迹象；C象征；D信号。句意：有确凿的证据证明火星上存在水，但不幸的是，仍然没有生命的迹象。故B正确。