单选题 A scientist usually directs his attention towards problems which he notices have no satisfactory explanation, and his curiosity makes him look for______ relationship even if the data available seem to be unconnected.

【正确答案】 D
【答案解析】underlying，“更深—层的”、“构成……的基础的”；underlining，”划线于……之下的”：underneath，“在……下面”、“在……底下”：undergoing，“经受的”、”经历了的”。