鼹鼠是出色的挖洞者，它们在地下建造复杂的隧道系统。

Moles are excellent ___burrowers, constructing intricate tunnel systems underground.

那些记者锲而不舍地深入调查了这起腐败案件。

The journalists were relentless ___burrowers, digging deep into the corruption case.