盖尔与克拉负的家都位于一个住宅小区里,相距只有100米.由于是新开发的住宅区,除了他们两家之外,暂时还没有其他人住进来,

Gail Devers
Yolanda Gail Devers (born November 19,1966 in Seattle,Washington,USA) is a three-time Olympic 100 m champion in athletics for the US Olympic Team.Devers grew up near National City,CA and graduated from Sweetwater High School in National City,CA.
A young talent in the 100 m and 100 m hurdles,Devers was in training for the 1988 Summer Olympics,started experiencing health problems,suffering from among others migraine and vision loss.She qualified for the Olympics 100 m hurdles,in which she was eliminated in the semi-finals,but her health continued to deteriorate even further.
In 1990,she was diagnosed with Graves' disease,and started radiation therapy.Amazingly,Devers recovered quickly and resumed training.At the 1991 World Championships,she won a silver medal in the 100 m hurdles.
At the 1992 Summer Olympics,Devers starred.She qualified for the final of the 100 m,which ended in an exciting finish,with five women finishing close (within 0.06 seconds).The photo finish showed Devers had narrowly beaten Jamaican Juliet Cuthbert.In the final of the 100 m hurdles,Devers' lead event,she seemed to be running towards a second gold medal when she hit the final hurdle and stumbled over the finish line in fifth place,leaving Voula Patoulidou from Greece as the upset winner.
In 1993,Devers won the 100 m World Championship title after - again - a photo finish win over Merlene Ottey in an apparent dead heat,and the 100 m hurdles title.She retained her hurdles title in 1995.
The 100 m final at the 1996 Summer Olympics was an almost exact repeat of the World Championships final three years before.Ottey and Devers again finished in the same time and did not know who had won the race.Again,both were awarded the same time,but Devers was judged to have finished first and became the first woman to retain the Olympic 100 m title since Wyomia Tyus.In the final of her favourite event,Devers again failed,as she finished fourth and outside of the medals.With the 4 x 100 m relay team,Devers won her third Olympic medal.
After these Olympics,Devers concentrated on the hurdles event,winning the World Championship again in 1999,but she had to forfeit for the semi-finals at the 2000 Summer Olympics.
Devers left competition in 2005 to give birth to a child with her husband and returned in 2006.
On February 2,2007,Devers edged 2004 Olympic champion Joanna Hayes to win the 60-meter hurdles event at the Millrose Games in 7.86 seconds - the best time in the world this season and just 0.12 off the record she set in 2003.
She is most easily identified by her long nails.

我来回答这个问题吧
个人认为, 这个问题不适合用圆盘定理做, 因为四个圆盘重叠得太厉害
先个你两种快捷的证法
1. A是非负矩阵, 由Perron-Frobenius定理知A至少有一个实特征值(就是谱半径), 但四阶实矩阵不可能有三个虚特征值, 因为虚根必成对
2. 直接算出det(A)

Anne's children were almost grown up, except for pretty, high-spirited Rilla. No one could resist her bright hazel eyes and dazzling smile. Rilla, almost fifteen, can't think any further ahe...