一块椎骨的椎体和椎弓围成（）
A.骶管裂孔
B.椎管
C.骶管
D.椎孔
E.椎间孔
参考答案：D
----It is nice. Never before___________ such a special drink!
---- I am glad you like it.
A．I have had
B．I had had
C．have I had
D．had I had
抗病性的机制有（）、（）、（）、（）。抗虫性的机制有（）、（）、（）。
