假定学生关系是S（S#,Sname,Ssex,Sage)，课程关系是C（C#,Cname,Cteacher)，学生选课关系是SC（S#,C#,Score), 要查找“选修‘COMPUTER’课程的女学生的姓名”，其正确的关系代数表达式是________。

A．R|X|R

B．

C．σf(R)

D．Πf(R)

A. X(A，B，C，D，E，G) B. X(A，B，C， D)C. X(R.A，B，R.C，D，S.A，S.C，E，G)D. X(B，D，E，G)

B、Select Sname From Student Where Sname Like ‘张%’;

C、Select Sname From Student Where Sname Like ‘张_’;

D、Select Sname From Student Where Sname Not Like ‘张_ _’;

A、Insert into CStud Values ( “98030104”, “张三丰”, “980301” );

B、Insert into CStud Values (98030104, “张三丰”, “980301”);

C、insert into CStud values (“98030104”, 张三丰, Null, Null, “03” , “980301”);

D、insert into CStud values (Null, “张三丰”, “980301”);

A.x2+y2=c(c∈R)

B.x2-y2=c(c∈R)

C.x2+y2=c2(c∈R)

D.x2-y2=c2(c∈R)