单项选择题

A.select e.empno,e.ename from emp e where e.sal <(select sum(x.vouch_amt)from expense x)and x.empno =e.empno;
B.select e.empno,e.ename from emp e where e.sal <(select x.vouch_amt from expense x where x.empno =e.empno);
C.select e.empno,e.ename from emp e where e.sal <(select sum(x.vouch_amt)from expense x where x.empno =e.empno);
D.select e.empno,e.ename from emp e where exists (select sum(x.vouch_amt)from expense x where x.empno =e.empno);