心外膜是（）
A.浆膜结构
B.心内膜凸向心腔折叠形成的薄片状突起
C.心脏传导系统
D.心房颗粒
E.心包壁层
参考答案：A
We had ____ fun at Mary’s birthday party last Sunday.
A．a plenty of
B．a great many
C．a large number of
D．a great deal of
