Do you think everyone _______ their weekends? [ ]

A. enjoys

B. enjoy

C. like

D. to enjoy

[说明]
设有三个关系：
BOOK (BNO，BNAME，PUBLISH_YEAR，PRICE，PRESS)
READ(RNO，RNAME，DUTY)
BR(BNO，RNO，RETURN_DAY)
试用关系代数表达式表示下列查询语句：

[问题3]
检索在1988年以前出版的书名。