〔R49〕 I am often seen on the ground;
Flat and smooth I am often found.
Only five letters make my name;
Forward or backwards, I'm the same.
〔译注〕 我常被看见在地上;
常被发现扁平而光滑;
只有五个字母造成我的名,
往前或往后看,我都是一个样。
〔提问〕 If I am an instrument (器物) for determining (判定) a surface (表面), what am I?
〔谜底〕
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