关系模型用______实现表与表之间的联系。
参考答案:公共属性
导致肺性脑病的因素有()。
A.CO2潴留
B.缺氧
C.酸碱平衡失调
D.脑组织pH下降
E.渗透压改变
-Hello, Mary! This is John. You must know why I _________ you.
-Oh, hello, John! I've waited for this call since last month.
A.called
B.am calling
C.was calling
D.have called