建筑物在10年到15年之后再夷为平地，这并不是前所未闻的事。

It is not unheard of for buildings to be razed after 10 or 15 years.

这几乎是前所未闻的，因为严肃的机器人学领域常以功能挂帅，而非外表。

Burick says that he spent a year honing their appearance, something almost unheard of in serious robotics, where function usually trumps form.

他在规定的时间和预算内完成了人口普查，这是一个前所未闻的成就。

He has brought the Census in on time and under budget, an unheard of accomplishment.

一次地震后接着发生更强的余震，这虽不是前所未闻，但确实罕有。

It is rare, though not unheard of, to have a quake followed by a larger aftershock.