下面语句是查询贷款的法人名称，下面哪条语句执行效率最高____。
选项：

A:select distinct cname from client c join loan l on c_.cno=l.cno
B:select cname from client c where exists(select * from loan l where l.cno=c_.cno)
C:select cname from client where cno in(select cno from loan)
D:select cname from client where cno not in(select cno from client except select cnoFrom loan)