touchstone|touchstones

这部作品被认为是现实主义文学的试金石。

This work is considered the ___touchstone of realist literature.

珠宝商用小块的试金石来检测黄金的纯度。

Jewelers use small pieces of ___touchstones to test the purity of gold.

客户满意度是我们服务的试金石。

Customer satisfaction is the ___touchstone of our service quality.