It must have fourteen lines, with three groups of four lines that set up the subject or problem of the poem.

VOA: special.2010.01.06

The problem of memory is just as important to the psychological dynamics of the fall of Adam and Eve, but as we will see when we look at Book Four, surely it's the problem of the poet's memory that's the most troubling in Paradise Lost.

记忆的问题的重要性与,亚当与夏娃堕落后心里的变化相当，但是我们将在第四册书看到，确实是诗人自己记忆的问题,困扰着《失乐园》这部作品。

耶鲁公开课 - 弥尔顿课程节选

He began to be a problem. In eighteen fifty-four, he was asked to leave the army.

VOA: special.2009.09.03

The last United Nations survey of Afghanistan's drug problem four years ago estimated the country's addicts to number about 200, 000.

CNN: Afghan junkies risk triggering AIDS explosion

The survey will tackle the problem in four ways.

BBC: Dark energy camera snaps first images ahead of survey

Al Gore has the Hillary problem, which four years hence may be powerful.

CNN: What the Loser Should Do