I agree with brofeelgood. 了 signals the end, and without it I would expect some follow-up action or clause.
Furthermore, 妈妈跑下楼来/弟弟跑回家去 ARE conversational scenarios, not some sentences you would find in a formal document.
I agree with brofeelgood. 了 signals the end, and without it I would expect some follow-up action or clause.
Furthermore, 妈妈跑下楼来/弟弟跑回家去 ARE conversational scenarios, not some sentences you would find in a formal document.
Yes. In your sentence 了 is not needed, especially in a composition. Just, it is still part of a sentence, or part of a cause-effect sequence, not a stand-alone statement.
Anyway, it's better to have a context to discuss this.