The army has made a ring around Tahrir Square...

军队已经包围了解放广场。

He was down once, but they made a ring round him, and fought their way along.

有一次他倒下了，但他们把他围成一圈，并一路奋战。

And you can't make a ring with one or two carbons, so the simplest cyclic hydrocarbon must be cyclopropane.

而且你不能用一个或两个碳组成一个环， 所以最简单的环烃必须是环丙烷。