She says she'll come, but I can't nail her down to a specifictime.
她说要来，但我无法让她敲定具体什么时候来。
《牛津词典》
2
It is difficult to understand how reduced predation would lead to sudden increases in Acanthaster numbers in several places at the same time in specific years.
很难理解捕食减少是如何导致在特定年份的同一时间内，几个地方的棘冠海星数量突然增加。
3
By contrast, the audience encounters an opera or a play over a specifictime, which is the duration of the performance.