Relatives of victims killed at the World Trade Center have commemorated the seventh anniversary of the Sept 11 attacks.

Moments of silence were observed to mark the times that two hijacked jetliners crashed into the twin towers and the moments the buildings collapsed.

Services were also held in Pennsylvania and at the Pentagon, where a new memorial was dedicated.

Maureen Hunt, wearing a T-shirt with a picture of her sister, Kathleen, a 9/11 victim, said that it was comforting to be at the ceremony with so many who have lost loved ones.

"This is a place for us to meet," said Hunt, who has come each year to pay her respects. "It is not getting easier to attend these ceremonies."

This year the solemn events unfold amid a presidential campaign, with John McCain and Barack Obama paying their respects at ground zero yesterday afternoon and later attending a New York City forum on public service.

Family members and students representing more than 90 countries that lost victims on Sept 11 read the names of more than 2,700 people killed in New York. Some mourners wondered if the remembrance would, or should, continue as it has indefinitely.

About 3,500 people attended last year's ceremony, down about 25 percent from 2006.

The ceremony moved to a park just east of ground zero last year because of construction at the trade center site. But family members are allowed to descend seven stories below ground to the site and touch the spot where their loved ones died.

Obama and McCain agreed weeks ago to pull their campaign ads for the day and were appearing together last night at a forum on volunteerism and service.

In Arlington, Virginia, Defense Secretary Robert Gates attended a ceremony dedicating the memorial at the Pentagon, the first of three major Sept 11 memorials to be completed.

President George W. Bush and First lady Laura Bush marked the anniversary during a moment of silence on the South Lawn of the White House. The president also attended the Pentagon memorial.

Questions:

1. Which memorial did George W. Bush and his wife attend?

2. How many people attended last year’s ceremony at ground zero?

3. What did Obama and McCain agree to do to mark Sept 11 this year?

Answers:

1. The Pentagon.

2. About 3,500.

3. To pull their campaign ads for the day and were appearing together last night at a forum on volunteerism and service.