将一枚硬币连掷3次，出现“两正，一反”的概率是多少？
解：P=。
I ______ my son _____ a doctor, but he wasn’t good enough at science.
A．hoped, became
B．hoped, could become
C．had hoped, would become
D．had hoped, would have become
现代物流具有哪些基本特征？
。
。