The problem is that catalysts and membranes have been expensive until recently.请问这里catalysts and membranes是最近才开始变贵,还是从以前到最近一直都是这么贵,还是说以前一直贵,但最近不贵了?还请教 until recently 是否有多种不同的用法?
...好,看到下面这个句子:One day when entering your home, your mother says your family is having dinner with the family of one of her old friends. “when”是引导的定语从句修饰“day”?还是one day是后面这个状语从句里的,为了强调提前了?谢谢老师。
When the concrete hardens, those otherwise harmful emissions are sequestered forever, before they even reach our atmosphere.句中otherwise什么用法,如何理解呢?如果去掉,语义有何变化?