怎么错了?

Question

//共有三个表:student,grade,course
procedure TForm3.Button1Click(Sender: TObject);var
 select,from,where,group, inwhere,studentidstr,courseidstr,:string;
begin
   studentidstr:=comboBox2.Text;//student 学号
   courseidstr:=ComboBox4.Text;//课程号
   
 select:='select  student.sid,student.sname,student.class,
     course.cname,grade.score '+'' ;
   from:='from student,grade,course'+'';
where:='where student.sid=grade.sid and course.cid=grade.cid and grade.score=';   group:='( select'+''+'min(score)'+''+'from grade,student,course';
              inwhere:='where student.sid='+studentidstr+''+'and course.cid='+courseidstr+')'
               
    studentgrade.Close;
    studentgrade.sql.Clear;
    studentgrade.sql.Add(select);
    studentgrade.sql.Add(from);
    studentgrade.sql.Add(where);
    studentgrade.sql.Add(group);
    studentgrade.sql.Add(inwhere);
    studentgrade.Prepare;
    studentgrade.open;
    studentgrade.Active:=true;
  end; ////////////////////////////////////////////////////

Answer 1

Invalid use of keyword.
Token:from
Line Number:4.

Answer 2

select:='select  student.sid,student.sname,student.class,
     course.cname,grade.score ';
   from:='from student,grade,course';
你把from用'   '括起来,肯定不对了

Answer 3

procedure TForm3.Button1Click(Sender: TObject);var
 select,from,where,group, inwhere,studentidstr,courseidstr,:string;
begin
   studentidstr:=comboBox2.Text;//student 学号
   courseidstr:=ComboBox4.Text;//课程号
   
 select:='select  student.sid,student.sname,student.class,
     course.cname,grade.score ';
   from:='from student,grade,course';
where:='where student.sid=grade.sid and course.cid=grade.cid and grade.score=';   group:='( select'+'min(score)'+'from grade,student,course';
              inwhere:='where student.sid='+studentidstr +'and course.cid='+courseidstr)'
               
    studentgrade.Close;
    studentgrade.sql.Clear;
    studentgrade.sql.Add(select);
    studentgrade.sql.Add(from);
    studentgrade.sql.Add(where);
    studentgrade.sql.Add(group);
    studentgrade.sql.Add(inwhere);
    studentgrade.Prepare;
    studentgrade.open;
    studentgrade.Active:=true;
  end;

Answer 4

select,from,where,group, inwhere,studentidstr,courseidstr,:string;
这里有个,号
应该是
select,from,where,group, inwhere,studentidstr,courseidstr:string;