21.   Safety standards have gradually become fairly uniform and customs barriers have fallen, meaning that moving cars across borders poses few problems.

22.   State regulators in Texas are warning that Mexican truckers could tear up highways and endanger drivers when trade barriers fall next month.

23.   That barrier fell long ago, as media moguls became infatuated with the idea that only partisan insiders can really explain what goes on in the backrooms of Washington.

24.   The outcome of the debate will likely have a strong impact on the future of the steel trade, in an era when tariff barriers are falling worldwide.

25.   Those barriers fall in September under a law permitting nationwide interstate banking.

26.   Thus begins another year of Carnival in Rio, the annual explosion of revelry when barriers briefly fall and this city turns upside down and inside out.

27.   Two distinctly separate tales of leverage and weight remind us again that barriers fall much faster for those with a healthy reservoir of celebrity, connections and cash.

28.   Undeterred by scrapes with the law, she flourished when social and legal barriers fell.

29.   Why, when countless racial barriers have fallen, does racial inequality endure?

30.   Yet these barriers have fallen, one by one, and young women today have forgotten how unfair it used to be.