But recent findings have suggested that tPA may be effective in saving brain tissue even if three to four and a half hours have passed.

VOA: special.2009.08.12

There had been a half century that had passed since any great modern epic or romance epic had even been produced.

在过去的半个世纪中,没有任何伟大的现代史诗或浪漫史诗出现。

耶鲁公开课 - 弥尔顿课程节选

The American Lung Association says half of the fifty states have passed smoke-free laws.

VOA: special.2009.05.27