问题 单项选择题

若关系中的某一属性组的值能唯一地标识一个元组。则称该属性组为( )。

A.主键
B.候选键
C.主属性
D.外部键

答案

参考答案:B

解析: 在一个关系中,凡是其取值能唯一地标识一个元组的属性或属性组,均称为候选键。如果关系中有多个候选键,则选择其中一个作为主键。组成候选键的任何一个属性均称为主属性。故本题选B。

阅读理解

B

ACTeen-Acting for Teens

The nation’s first on-camera acting program developed for teens(ages 13—15, 16—20). Now celebrating our 30th year. June, July, August, or。Saturday summer academies offer full or part-time curriculum. 14 + electives, including film & television acting, theater, musical theater, auditioning, Shakespeare, speech & voice, movement, script writing.

Working grades, small classes(12 maximum per workshop). Safe, convenient location. Application required. Out of town applicants may submit long distance application.

Cost/Week: $500一$649

Indianhead Ranch

Sharpen your H unting Skills over one or two weeks at Indianhead Ranch in Del Rio, Texas. You will experience the outdoors, expand your knowledge in gun safety and learn practical camping hunting and survival skills.

Cost/Week: $1000一$1999

Vermont Adventure Camps

Six-Day Adventure Camps

We offer 8 six-day adventure camps for teens l1 to 13. The kids go stay in rustic cabins at our camping site in Andover VT and on adventures each day. A discount of 10% will be given to the team with over 3 persons.

Two-Week Adventure Camps

We also offer 4 two-week adventure camps for teens 14 to 17. The teens will go on an adventure each day and then come back to our quaint Adventure Lodge.

Cost/Week: $650

International ESL Camp

The site is in close proximity to New York, Philadelphia, and Princeton University. Campers will receive three hours per day of English language instruction, a full range of planned activities including sports, arts and crafts, and weekly excursions.

Cost/Week: $650一$999

59. According to the passages, which camp offers hunting skills?

A. Vermont Adventure Camps.        B. Indianhead Ranch.

C. Acting for Teens.                 D. International ESL Camp.

60. Which of the following statements about ACTeeen is TRUE?

A. Applicants out of town cannot submit.

B. There i s no need for application to the camp.

C. The camp lasts until September.

D. Its curriculum includes script writing.

61. If Tom plans to send his 4 children to join Six-Day Adventure Camps, how much should he pay?

A. 2,340.         B. 2,600.          C. 260.           D. 2,860.

单项选择题