عَادَ بَعْضُ الطُّلَّابِ مُبَكِّرِينَ. كَثُفَتِ السُّحُبُ فَوْقَ الْمَرْصَدِ.
Some students returned early. Clouds had grown thick above the observatory.
The first report naturally raises “Why did they return early?” The second answers that implied question about cause. Its separation from the first thus creates explanatory resumption rather than ordinary coordination of independent reports.
An analyst must still justify the implied question from context. If the sentences merely convey two separately relevant observations, a different analysis may be appropriate.