Sunday, an estimated 275,000 people will crowd the banks of the Charles River for one of the following events:

A. A World Cup soccer game.

B. Easter Mass at the Vatican.

C. A Prince concert.

D. The 24th Annual Head of the Charles Regatta.

Since the World Cup won't be held in the United States until 1992, Easter is six months away and Prince is in Worcester, there's only one answer.

The Head--Boston's annual rite of fall.

This year, the Head will feature more than 3500 rowers in 840 boats, competing in a total of 16 individual and crew races. The course begins at the Boston University Bridge and spans three miles to the finish line near the Herter Center on Soldiers Field Road.

The first race, the Club Singles, is slated for 8:40 a.m. Fourteen races and seven hours later, the Championship Eights event will close out the day's schedule.

All results of the races will be officially announced at the Cambridge Boat House on Memorial Drive.

The regatta, which 400 volunteers have helped to organize, will feature the world's best rowers, including some Olympic medalists.

Andy Sudduth '83, who captured a silver medal in the single sculling in the 1984 Olympics, and Anne Marden, a silver medalist in women's sculling in Seoul, have entered the Regatta. Marden is the defending champion in the Women's Championship Single.

Regatta organizers hoped that the world-class East German team would participate in this year's events, but the East Germans have decided not to race because they are on a one-month vacation after a successful performance in Seoul.

"The entire team takes one month off together," said Anna P. Jones, publicity spokesperson for the Head. "They're cooling out."

The U.S. Men's Eight will not race as an entire crew. Four members of the crew, however, will row for the Penn Athletic Club.