Final answer:
A moment of silence is typically observed at the memorial service beginning at 8:46 am, the time the first plane struck the first tower, to honor the victims of the September 11 attacks.
Step-by-step explanation:
At the memorial service, which begins each year at 8:46 am to mark the exact time when the first plane struck the North Tower (the first tower) of the World Trade Center on September 11, 2001, participants usually observe a moment of silence. This moment of silence honors the memory of the nearly 3,000 victims who lost their lives due to the terrorist attacks on that day. The service often includes reading the names of those who perished, performances by musicians, and other commemorative activities designed to pay tribute to the victims and reflect on the impact of the events.