心肌细胞的收缩性有以下特点是什么?
参考答案:
(1)对细胞外液中Ca2+浓度的依赖性
(2)同步收缩(“全”或“无”收缩)
(3)不发生强直收缩
(4)期前收缩与代偿性间歇
I've ________ the habit of calling in on my grandparents on my way home from school. [ ]
A. come into
B. gone into
C. got into
D. run into
采购实际上是商流与物流相统一的过程。