原SQL：
select avg(degree) from score where cno like '3%' group by Cno having count(*)>=5
Linq:
(
from s in Scores
where s.CNO.StartsWith("3")
group s by s.CNO
into cc
orderby cc.Count() >= 5
....
如何写？linq to sql
0
from s in Scores
where s.CNO.StartsWith("3")
group s by s.CNO
into cc
where cc.Count() >= 5
select cc.Average( c => c.DEGREE)